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<li class="toctree-l2"><a class="reference internal" href="whatsnew.html#what-s-new-in-version-0-15-0-2015-07-25">What&#8217;s new in version 0.15.0 (2015-07-25)</a></li>
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<li class="toctree-l1"><a class="reference internal" href="overview.html">Overview: Easy, clean, reliable Python 2/3 compatibility</a><ul>
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<li class="toctree-l1 current"><a class="current reference internal" href="">Cheat Sheet: Writing Python 2-3 compatible code</a><ul>
<li class="toctree-l2"><a class="reference internal" href="#setup">Setup</a></li>
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<li class="toctree-l3"><a class="reference internal" href="#print">print</a></li>
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<li class="toctree-l2"><a class="reference internal" href="imports.html#using-python-2-only-dependencies-on-python-3">Using Python 2-only dependencies on Python 3</a></li>
<li class="toctree-l2"><a class="reference internal" href="imports.html#should-i-import-unicode-literals">Should I import unicode_literals?</a><ul>
<li class="toctree-l3"><a class="reference internal" href="imports.html#benefits">Benefits</a></li>
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<li class="toctree-l3"><a class="reference internal" href="imports.html#others-perspectives">Others&#8217; perspectives</a></li>
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<li class="toctree-l2"><a class="reference internal" href="imports.html#next-steps">Next steps</a></li>
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<li class="toctree-l1"><a class="reference internal" href="what_else.html">What else you need to know</a><ul>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#bytes">bytes</a></li>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#str">str</a></li>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#dict">dict</a><ul>
<li class="toctree-l3"><a class="reference internal" href="what_else.html#memory-efficiency-and-alternatives">Memory-efficiency and alternatives</a></li>
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<li class="toctree-l2"><a class="reference internal" href="what_else.html#int">int</a></li>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#isinstance">isinstance</a></li>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#passing-data-to-from-python-2-libraries">Passing data to/from Python 2 libraries</a></li>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#native-string-type">Native string type</a></li>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#open">open()</a></li>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#custom-str-methods">Custom __str__ methods</a></li>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#custom-iterators">Custom iterators</a></li>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#binding-a-method-to-a-class">Binding a method to a class</a></li>
<li class="toctree-l2"><a class="reference internal" href="what_else.html#metaclasses">Metaclasses</a></li>
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<li class="toctree-l1"><a class="reference internal" href="automatic_conversion.html">Automatic conversion to Py2/3</a><ul>
<li class="toctree-l2"><a class="reference internal" href="automatic_conversion.html#futurize-py2-to-py2-3"><code class="docutils literal"><span class="pre">futurize</span></code>: Py2 to Py2/3</a><ul>
<li class="toctree-l3"><a class="reference internal" href="automatic_conversion.html#stage-1-safe-fixes">Stage 1: &#8220;safe&#8221; fixes</a></li>
<li class="toctree-l3"><a class="reference internal" href="automatic_conversion.html#stage-2-py3-style-code-with-wrappers-for-py2">Stage 2: Py3-style code with wrappers for Py2</a></li>
<li class="toctree-l3"><a class="reference internal" href="automatic_conversion.html#separating-text-from-bytes">Separating text from bytes</a></li>
<li class="toctree-l3"><a class="reference internal" href="automatic_conversion.html#post-conversion">Post-conversion</a></li>
</ul>
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<li class="toctree-l2"><a class="reference internal" href="automatic_conversion.html#futurize-quick-start-guide"><code class="docutils literal"><span class="pre">futurize</span></code> quick-start guide</a><ul>
<li class="toctree-l3"><a class="reference internal" href="automatic_conversion.html#step-0-setup">Step 0: setup</a></li>
<li class="toctree-l3"><a class="reference internal" href="automatic_conversion.html#step-1-modern-py2-code">Step 1: modern Py2 code</a></li>
<li class="toctree-l3"><a class="reference internal" href="automatic_conversion.html#step-2-working-py3-code-that-still-supports-py2">Step 2: working Py3 code that still supports Py2</a></li>
</ul>
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<li class="toctree-l2"><a class="reference internal" href="automatic_conversion.html#pasteurize-py3-to-py2-3"><code class="docutils literal"><span class="pre">pasteurize</span></code>: Py3 to Py2/3</a></li>
<li class="toctree-l2"><a class="reference internal" href="automatic_conversion.html#known-limitations">Known limitations</a></li>
</ul>
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<li class="toctree-l1"><a class="reference internal" href="faq.html">Frequently Asked Questions (FAQ)</a><ul>
<li class="toctree-l2"><a class="reference internal" href="faq.html#who-is-this-for">Who is this for?</a></li>
<li class="toctree-l2"><a class="reference internal" href="faq.html#why-upgrade-to-python-3">Why upgrade to Python 3?</a></li>
<li class="toctree-l2"><a class="reference internal" href="faq.html#porting-philosophy">Porting philosophy</a><ul>
<li class="toctree-l3"><a class="reference internal" href="faq.html#why-write-python-3-style-code">Why write Python 3-style code?</a></li>
<li class="toctree-l3"><a class="reference internal" href="faq.html#can-t-i-just-roll-my-own-py2-3-compatibility-layer">Can&#8217;t I just roll my own Py2/3 compatibility layer?</a></li>
<li class="toctree-l3"><a class="reference internal" href="faq.html#what-inspired-this-project">What inspired this project?</a></li>
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<li class="toctree-l2"><a class="reference internal" href="faq.html#maturity">Maturity</a><ul>
<li class="toctree-l3"><a class="reference internal" href="faq.html#how-well-has-it-been-tested">How well has it been tested?</a></li>
<li class="toctree-l3"><a class="reference internal" href="faq.html#is-the-api-stable">Is the API stable?</a></li>
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<li class="toctree-l2"><a class="reference internal" href="faq.html#relationship-between-python-future-and-other-compatibility-tools">Relationship between python-future and other compatibility tools</a><ul>
<li class="toctree-l3"><a class="reference internal" href="faq.html#how-does-this-relate-to-2to3">How does this relate to <code class="docutils literal"><span class="pre">2to3</span></code>?</a></li>
<li class="toctree-l3"><a class="reference internal" href="faq.html#can-i-maintain-a-python-2-codebase-and-use-2to3-to-automatically-convert-to-python-3-in-the-setup-script">Can I maintain a Python 2 codebase and use 2to3 to automatically convert to Python 3 in the setup script?</a></li>
<li class="toctree-l3"><a class="reference internal" href="faq.html#what-is-the-relationship-between-future-and-six">What is the relationship between <code class="docutils literal"><span class="pre">future</span></code> and <code class="docutils literal"><span class="pre">six</span></code>?</a></li>
<li class="toctree-l3"><a class="reference internal" href="faq.html#what-is-the-relationship-between-python-future-and-python-modernize">What is the relationship between <code class="docutils literal"><span class="pre">python-future</span></code> and <code class="docutils literal"><span class="pre">python-modernize</span></code>?</a></li>
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<li class="toctree-l2"><a class="reference internal" href="faq.html#platform-and-version-support">Platform and version support</a><ul>
<li class="toctree-l3"><a class="reference internal" href="faq.html#which-versions-of-python-does-python-future-support">Which versions of Python does <code class="docutils literal"><span class="pre">python-future</span></code> support?</a></li>
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<li class="toctree-l2"><a class="reference internal" href="faq.html#support">Support</a><ul>
<li class="toctree-l3"><a class="reference internal" href="faq.html#is-there-a-mailing-list">Is there a mailing list?</a></li>
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</li>
<li class="toctree-l2"><a class="reference internal" href="#custom-class-behaviour">Custom class behaviour</a><ul>
<li class="toctree-l3"><a class="reference internal" href="#custom-iterators">Custom iterators</a></li>
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  <div class="section" id="cheat-sheet-writing-python-2-3-compatible-code">
<span id="compatible-idioms"></span><h1>Cheat Sheet: Writing Python 2-3 compatible code<a class="headerlink" href="#cheat-sheet-writing-python-2-3-compatible-code" title="Permalink to this headline">¶</a></h1>
<ul class="simple">
<li><strong>Copyright (c):</strong> 2013-2015 Python Charmers Pty Ltd, Australia.</li>
<li><strong>Author:</strong> Ed Schofield.</li>
<li><strong>Licence:</strong> Creative Commons Attribution.</li>
</ul>
<p>A PDF version is here: <a class="reference external" href="http://python-future.org/compatible_idioms.pdf">http://python-future.org/compatible_idioms.pdf</a></p>
<p>This notebook shows you idioms for writing future-proof code that is
compatible with both versions of Python: 2 and 3. It accompanies Ed
Schofield&#8217;s talk at PyCon AU 2014, &#8220;Writing 2/3 compatible code&#8221;. (The
video is here: <a class="reference external" href="http://www.youtube.com/watch?v=KOqk8j11aAI&amp;t=10m14s">http://www.youtube.com/watch?v=KOqk8j11aAI&amp;t=10m14s</a>.)</p>
<p>Minimum versions:</p>
<ul class="simple">
<li>Python 2: 2.6+</li>
<li>Python 3: 3.3+</li>
</ul>
<div class="section" id="setup">
<h2>Setup<a class="headerlink" href="#setup" title="Permalink to this headline">¶</a></h2>
<p>The imports below refer to these <code class="docutils literal"><span class="pre">pip</span></code>-installable packages on PyPI:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">future</span>        <span class="c"># pip install future</span>
<span class="kn">import</span> <span class="nn">builtins</span>      <span class="c"># pip install future</span>
<span class="kn">import</span> <span class="nn">past</span>          <span class="c"># pip install future</span>
<span class="kn">import</span> <span class="nn">six</span>           <span class="c"># pip install six</span>
</pre></div>
</div>
<p>The following scripts are also <code class="docutils literal"><span class="pre">pip</span></code>-installable:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">futurize</span>             <span class="c"># pip install future</span>
<span class="n">pasteurize</span>           <span class="c"># pip install future</span>
</pre></div>
</div>
<p>See <a class="reference external" href="http://python-future.org">http://python-future.org</a> and <a class="reference external" href="https://pythonhosted.org/six/">https://pythonhosted.org/six/</a> for more
information.</p>
</div>
<div class="section" id="essential-syntax-differences">
<h2>Essential syntax differences<a class="headerlink" href="#essential-syntax-differences" title="Permalink to this headline">¶</a></h2>
<div class="section" id="print">
<h3>print<a class="headerlink" href="#print" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre># Python 2 only:
print &#39;Hello&#39;
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="k">print</span><span class="p">(</span><span class="s">&#39;Hello&#39;</span><span class="p">)</span>
</pre></div>
</div>
<p>To print multiple strings, import <code class="docutils literal"><span class="pre">print_function</span></code> to prevent Py2 from
interpreting it as a tuple:</p>
<div class="code python highlight-python"><div class="highlight"><pre># Python 2 only:
print &#39;Hello&#39;, &#39;Guido&#39;
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</span>    <span class="c"># (at top of module)</span>

<span class="k">print</span><span class="p">(</span><span class="s">&#39;Hello&#39;</span><span class="p">,</span> <span class="s">&#39;Guido&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">print</span> <span class="o">&gt;&gt;</span> <span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&#39;Hello&#39;</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</span>

<span class="k">print</span><span class="p">(</span><span class="s">&#39;Hello&#39;</span><span class="p">,</span> <span class="nb">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre># Python 2 only:
print &#39;Hello&#39;,
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</span>

<span class="k">print</span><span class="p">(</span><span class="s">&#39;Hello&#39;</span><span class="p">,</span> <span class="n">end</span><span class="o">=</span><span class="s">&#39;&#39;</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="raising-exceptions">
<h3>Raising exceptions<a class="headerlink" href="#raising-exceptions" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre># Python 2 only:
raise ValueError, &quot;dodgy value&quot;
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="k">raise</span> <span class="ne">ValueError</span><span class="p">(</span><span class="s">&quot;dodgy value&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>Raising exceptions with a traceback:</p>
<div class="code python highlight-python"><div class="highlight"><pre># Python 2 only:
traceback = sys.exc_info()[2]
raise ValueError, &quot;dodgy value&quot;, traceback
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only:</span>
<span class="k">raise</span> <span class="ne">ValueError</span><span class="p">(</span><span class="s">&quot;dodgy value&quot;</span><span class="p">)</span><span class="o">.</span><span class="n">with_traceback</span><span class="p">()</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 1</span>
<span class="kn">from</span> <span class="nn">six</span> <span class="kn">import</span> <span class="n">reraise</span> <span class="k">as</span> <span class="n">raise_</span>
<span class="c"># or</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">raise_</span>

<span class="n">traceback</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">exc_info</span><span class="p">()[</span><span class="mi">2</span><span class="p">]</span>
<span class="n">raise_</span><span class="p">(</span><span class="ne">ValueError</span><span class="p">,</span> <span class="s">&quot;dodgy value&quot;</span><span class="p">,</span> <span class="n">traceback</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 2</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">raise_with_traceback</span>

<span class="n">raise_with_traceback</span><span class="p">(</span><span class="ne">ValueError</span><span class="p">(</span><span class="s">&quot;dodgy value&quot;</span><span class="p">))</span>
</pre></div>
</div>
<p>Exception chaining (PEP 3134):</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Setup:</span>
<span class="k">class</span> <span class="nc">DatabaseError</span><span class="p">(</span><span class="ne">Exception</span><span class="p">):</span>
    <span class="k">pass</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only</span>
<span class="k">class</span> <span class="nc">FileDatabase</span><span class="p">:</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">filename</span><span class="p">):</span>
        <span class="k">try</span><span class="p">:</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">file</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">filename</span><span class="p">)</span>
        <span class="k">except</span> <span class="ne">IOError</span> <span class="k">as</span> <span class="n">exc</span><span class="p">:</span>
            <span class="k">raise</span> <span class="n">DatabaseError</span><span class="p">(</span><span class="s">&#39;failed to open&#39;</span><span class="p">)</span> <span class="kn">from</span> <span class="nn">exc</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">raise_from</span>

<span class="k">class</span> <span class="nc">FileDatabase</span><span class="p">:</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">filename</span><span class="p">):</span>
        <span class="k">try</span><span class="p">:</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">file</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">filename</span><span class="p">)</span>
        <span class="k">except</span> <span class="ne">IOError</span> <span class="k">as</span> <span class="n">exc</span><span class="p">:</span>
            <span class="n">raise_from</span><span class="p">(</span><span class="n">DatabaseError</span><span class="p">(</span><span class="s">&#39;failed to open&#39;</span><span class="p">),</span> <span class="n">exc</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Testing the above:</span>
<span class="k">try</span><span class="p">:</span>
    <span class="n">fd</span> <span class="o">=</span> <span class="n">FileDatabase</span><span class="p">(</span><span class="s">&#39;non_existent_file.txt&#39;</span><span class="p">)</span>
<span class="k">except</span> <span class="ne">Exception</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
    <span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">e</span><span class="o">.</span><span class="n">__cause__</span><span class="p">,</span> <span class="ne">IOError</span><span class="p">)</span>    <span class="c"># FileNotFoundError on Py3.3+ inherits from IOError</span>
</pre></div>
</div>
</div>
<div class="section" id="catching-exceptions">
<h3>Catching exceptions<a class="headerlink" href="#catching-exceptions" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre># Python 2 only:
try:
    ...
except ValueError, e:
    ...
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="k">try</span><span class="p">:</span>
    <span class="o">...</span>
<span class="k">except</span> <span class="ne">ValueError</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
    <span class="o">...</span>
</pre></div>
</div>
</div>
<div class="section" id="division">
<h3>Division<a class="headerlink" href="#division" title="Permalink to this headline">¶</a></h3>
<p>Integer division (rounding down):</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">assert</span> <span class="mi">2</span> <span class="o">/</span> <span class="mi">3</span> <span class="o">==</span> <span class="mi">0</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="k">assert</span> <span class="mi">2</span> <span class="o">//</span> <span class="mi">3</span> <span class="o">==</span> <span class="mi">0</span>
</pre></div>
</div>
<p>&#8220;True division&#8221; (float division):</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only:</span>
<span class="k">assert</span> <span class="mi">3</span> <span class="o">/</span> <span class="mi">2</span> <span class="o">==</span> <span class="mf">1.5</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">division</span>    <span class="c"># (at top of module)</span>

<span class="k">assert</span> <span class="mi">3</span> <span class="o">/</span> <span class="mi">2</span> <span class="o">==</span> <span class="mf">1.5</span>
</pre></div>
</div>
<p>&#8220;Old division&#8221; (i.e. compatible with Py2 behaviour):</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="n">a</span> <span class="o">=</span> <span class="n">b</span> <span class="o">/</span> <span class="n">c</span>            <span class="c"># with any types</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">past.utils</span> <span class="kn">import</span> <span class="n">old_div</span>

<span class="n">a</span> <span class="o">=</span> <span class="n">old_div</span><span class="p">(</span><span class="n">b</span><span class="p">,</span> <span class="n">c</span><span class="p">)</span>    <span class="c"># always same as / on Py2</span>
</pre></div>
</div>
</div>
<div class="section" id="long-integers">
<h3>Long integers<a class="headerlink" href="#long-integers" title="Permalink to this headline">¶</a></h3>
<p>Short integers are gone in Python 3 and <code class="docutils literal"><span class="pre">long</span></code> has become <code class="docutils literal"><span class="pre">int</span></code>
(without the trailing <code class="docutils literal"><span class="pre">L</span></code> in the <code class="docutils literal"><span class="pre">repr</span></code>).</p>
<div class="code python highlight-python"><div class="highlight"><pre># Python 2 only
k = 9223372036854775808L

# Python 2 and 3:
k = 9223372036854775808
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre># Python 2 only
bigint = 1L

# Python 2 and 3
from builtins import int
bigint = int(1)
</pre></div>
</div>
<p>To test whether a value is an integer (of any kind):</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="p">(</span><span class="nb">int</span><span class="p">,</span> <span class="nb">long</span><span class="p">)):</span>
    <span class="o">...</span>

<span class="c"># Python 3 only:</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="nb">int</span><span class="p">):</span>
    <span class="o">...</span>

<span class="c"># Python 2 and 3: option 1</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">int</span>    <span class="c"># subclass of long on Py2</span>

<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="nb">int</span><span class="p">):</span>             <span class="c"># matches both int and long on Py2</span>
    <span class="o">...</span>

<span class="c"># Python 2 and 3: option 2</span>
<span class="kn">from</span> <span class="nn">past.builtins</span> <span class="kn">import</span> <span class="nb">long</span>

<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="p">(</span><span class="nb">int</span><span class="p">,</span> <span class="nb">long</span><span class="p">)):</span>
    <span class="o">...</span>
</pre></div>
</div>
</div>
<div class="section" id="octal-constants">
<h3>Octal constants<a class="headerlink" href="#octal-constants" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre>0644     # Python 2 only
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="mi">0</span><span class="n">o644</span>    <span class="c"># Python 2 and 3</span>
</pre></div>
</div>
</div>
<div class="section" id="backtick-repr">
<h3>Backtick repr<a class="headerlink" href="#backtick-repr" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre>`x`      # Python 2 only
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="nb">repr</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>  <span class="c"># Python 2 and 3</span>
</pre></div>
</div>
</div>
<div class="section" id="metaclasses">
<h3>Metaclasses<a class="headerlink" href="#metaclasses" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">BaseForm</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">pass</span>

<span class="k">class</span> <span class="nc">FormType</span><span class="p">(</span><span class="nb">type</span><span class="p">):</span>
    <span class="k">pass</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">class</span> <span class="nc">Form</span><span class="p">(</span><span class="n">BaseForm</span><span class="p">):</span>
    <span class="n">__metaclass__</span> <span class="o">=</span> <span class="n">FormType</span>
    <span class="k">pass</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only:</span>
<span class="k">class</span> <span class="nc">Form</span><span class="p">(</span><span class="n">BaseForm</span><span class="p">,</span> <span class="n">metaclass</span><span class="o">=</span><span class="n">FormType</span><span class="p">):</span>
    <span class="k">pass</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">six</span> <span class="kn">import</span> <span class="n">with_metaclass</span>
<span class="c"># or</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">with_metaclass</span>

<span class="k">class</span> <span class="nc">Form</span><span class="p">(</span><span class="n">with_metaclass</span><span class="p">(</span><span class="n">FormType</span><span class="p">,</span> <span class="n">BaseForm</span><span class="p">)):</span>
    <span class="k">pass</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="strings-and-bytes">
<h2>Strings and bytes<a class="headerlink" href="#strings-and-bytes" title="Permalink to this headline">¶</a></h2>
<div class="section" id="unicode-text-string-literals">
<h3>Unicode (text) string literals<a class="headerlink" href="#unicode-text-string-literals" title="Permalink to this headline">¶</a></h3>
<p>If you are upgrading an existing Python 2 codebase, it may be preferable
to mark up all string literals as unicode explicitly with <code class="docutils literal"><span class="pre">u</span></code>
prefixes:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only</span>
<span class="n">s1</span> <span class="o">=</span> <span class="s">&#39;The Zen of Python&#39;</span>
<span class="n">s2</span> <span class="o">=</span> <span class="s">u&#39;きたないのよりきれいな方がいい</span><span class="se">\n</span><span class="s">&#39;</span>

<span class="c"># Python 2 and 3</span>
<span class="n">s1</span> <span class="o">=</span> <span class="s">u&#39;The Zen of Python&#39;</span>
<span class="n">s2</span> <span class="o">=</span> <span class="s">u&#39;きたないのよりきれいな方がいい</span><span class="se">\n</span><span class="s">&#39;</span>
</pre></div>
</div>
<p>The <code class="docutils literal"><span class="pre">futurize</span></code> and <code class="docutils literal"><span class="pre">python-modernize</span></code> tools do not currently offer
an option to do this automatically.</p>
<p>If you are writing code for a new project or new codebase, you can use
this idiom to make all string literals in a module unicode strings:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">unicode_literals</span>    <span class="c"># at top of module</span>

<span class="n">s1</span> <span class="o">=</span> <span class="s">&#39;The Zen of Python&#39;</span>
<span class="n">s2</span> <span class="o">=</span> <span class="s">&#39;きたないのよりきれいな方がいい</span><span class="se">\n</span><span class="s">&#39;</span>
</pre></div>
</div>
<p>See <a class="reference external" href="http://python-future.org/unicode_literals.html">http://python-future.org/unicode_literals.html</a> for more discussion
on which style to use.</p>
</div>
<div class="section" id="byte-string-literals">
<h3>Byte-string literals<a class="headerlink" href="#byte-string-literals" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only</span>
<span class="n">s</span> <span class="o">=</span> <span class="s">&#39;This must be a byte-string&#39;</span>

<span class="c"># Python 2 and 3</span>
<span class="n">s</span> <span class="o">=</span> <span class="n">b</span><span class="s">&#39;This must be a byte-string&#39;</span>
</pre></div>
</div>
<p>To loop over a byte-string with possible high-bit characters, obtaining
each character as a byte-string of length 1:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">for</span> <span class="n">bytechar</span> <span class="ow">in</span> <span class="s">&#39;byte-string with high-bit chars like </span><span class="se">\xf9</span><span class="s">&#39;</span><span class="p">:</span>
    <span class="o">...</span>

<span class="c"># Python 3 only:</span>
<span class="k">for</span> <span class="n">myint</span> <span class="ow">in</span> <span class="n">b</span><span class="s">&#39;byte-string with high-bit chars like </span><span class="se">\xf9</span><span class="s">&#39;</span><span class="p">:</span>
    <span class="n">bytechar</span> <span class="o">=</span> <span class="nb">bytes</span><span class="p">([</span><span class="n">myint</span><span class="p">])</span>

<span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">bytes</span>
<span class="k">for</span> <span class="n">myint</span> <span class="ow">in</span> <span class="nb">bytes</span><span class="p">(</span><span class="n">b</span><span class="s">&#39;byte-string with high-bit chars like </span><span class="se">\xf9</span><span class="s">&#39;</span><span class="p">):</span>
    <span class="n">bytechar</span> <span class="o">=</span> <span class="nb">bytes</span><span class="p">([</span><span class="n">myint</span><span class="p">])</span>
</pre></div>
</div>
<p>As an alternative, <code class="docutils literal"><span class="pre">chr()</span></code> and <code class="docutils literal"><span class="pre">.encode('latin-1')</span></code> can be used to
convert an int into a 1-char byte string:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only:</span>
<span class="k">for</span> <span class="n">myint</span> <span class="ow">in</span> <span class="n">b</span><span class="s">&#39;byte-string with high-bit chars like </span><span class="se">\xf9</span><span class="s">&#39;</span><span class="p">:</span>
    <span class="n">char</span> <span class="o">=</span> <span class="nb">chr</span><span class="p">(</span><span class="n">myint</span><span class="p">)</span>    <span class="c"># returns a unicode string</span>
    <span class="n">bytechar</span> <span class="o">=</span> <span class="n">char</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s">&#39;latin-1&#39;</span><span class="p">)</span>

<span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">bytes</span><span class="p">,</span> <span class="nb">chr</span>
<span class="k">for</span> <span class="n">myint</span> <span class="ow">in</span> <span class="nb">bytes</span><span class="p">(</span><span class="n">b</span><span class="s">&#39;byte-string with high-bit chars like </span><span class="se">\xf9</span><span class="s">&#39;</span><span class="p">):</span>
    <span class="n">char</span> <span class="o">=</span> <span class="nb">chr</span><span class="p">(</span><span class="n">myint</span><span class="p">)</span>    <span class="c"># returns a unicode string</span>
    <span class="n">bytechar</span> <span class="o">=</span> <span class="n">char</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s">&#39;latin-1&#39;</span><span class="p">)</span>    <span class="c"># forces returning a byte str</span>
</pre></div>
</div>
</div>
<div class="section" id="basestring">
<h3>basestring<a class="headerlink" href="#basestring" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="n">a</span> <span class="o">=</span> <span class="s">u&#39;abc&#39;</span>
<span class="n">b</span> <span class="o">=</span> <span class="s">&#39;def&#39;</span>
<span class="k">assert</span> <span class="p">(</span><span class="nb">isinstance</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="nb">basestring</span><span class="p">)</span> <span class="ow">and</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">b</span><span class="p">,</span> <span class="nb">basestring</span><span class="p">))</span>

<span class="c"># Python 2 and 3: alternative 1</span>
<span class="kn">from</span> <span class="nn">past.builtins</span> <span class="kn">import</span> <span class="nb">basestring</span>    <span class="c"># pip install future</span>

<span class="n">a</span> <span class="o">=</span> <span class="s">u&#39;abc&#39;</span>
<span class="n">b</span> <span class="o">=</span> <span class="n">b</span><span class="s">&#39;def&#39;</span>
<span class="k">assert</span> <span class="p">(</span><span class="nb">isinstance</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="nb">basestring</span><span class="p">)</span> <span class="ow">and</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">b</span><span class="p">,</span> <span class="nb">basestring</span><span class="p">))</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 2: refactor the code to avoid considering</span>
<span class="c"># byte-strings as strings.</span>

<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">str</span>
<span class="n">a</span> <span class="o">=</span> <span class="s">u&#39;abc&#39;</span>
<span class="n">b</span> <span class="o">=</span> <span class="n">b</span><span class="s">&#39;def&#39;</span>
<span class="n">c</span> <span class="o">=</span> <span class="n">b</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="nb">str</span><span class="p">)</span> <span class="ow">and</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">c</span><span class="p">,</span> <span class="nb">str</span><span class="p">)</span>
<span class="c"># ...</span>
</pre></div>
</div>
</div>
<div class="section" id="unicode">
<h3>unicode<a class="headerlink" href="#unicode" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="n">templates</span> <span class="o">=</span> <span class="p">[</span><span class="s">u&quot;blog/blog_post_detail_</span><span class="si">%s</span><span class="s">.html&quot;</span> <span class="o">%</span> <span class="nb">unicode</span><span class="p">(</span><span class="n">slug</span><span class="p">)]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 1</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">str</span>
<span class="n">templates</span> <span class="o">=</span> <span class="p">[</span><span class="s">u&quot;blog/blog_post_detail_</span><span class="si">%s</span><span class="s">.html&quot;</span> <span class="o">%</span> <span class="nb">str</span><span class="p">(</span><span class="n">slug</span><span class="p">)]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 2</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">str</span> <span class="k">as</span> <span class="n">text</span>
<span class="n">templates</span> <span class="o">=</span> <span class="p">[</span><span class="s">u&quot;blog/blog_post_detail_</span><span class="si">%s</span><span class="s">.html&quot;</span> <span class="o">%</span> <span class="n">text</span><span class="p">(</span><span class="n">slug</span><span class="p">)]</span>
</pre></div>
</div>
</div>
<div class="section" id="stringio">
<h3>StringIO<a class="headerlink" href="#stringio" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">from</span> <span class="nn">StringIO</span> <span class="kn">import</span> <span class="n">StringIO</span>
<span class="c"># or:</span>
<span class="kn">from</span> <span class="nn">cStringIO</span> <span class="kn">import</span> <span class="n">StringIO</span>

<span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">io</span> <span class="kn">import</span> <span class="n">BytesIO</span>     <span class="c"># for handling byte strings</span>
<span class="kn">from</span> <span class="nn">io</span> <span class="kn">import</span> <span class="n">StringIO</span>    <span class="c"># for handling unicode strings</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="imports-relative-to-a-package">
<h2>Imports relative to a package<a class="headerlink" href="#imports-relative-to-a-package" title="Permalink to this headline">¶</a></h2>
<p>Suppose the package is:</p>
<div class="highlight-python"><div class="highlight"><pre>mypackage/
    __init__.py
    submodule1.py
    submodule2.py
</pre></div>
</div>
<p>and the code below is in <code class="docutils literal"><span class="pre">submodule1.py</span></code>:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">import</span> <span class="nn">submodule2</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">.</span> <span class="kn">import</span> <span class="n">submodule2</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="c"># To make Py2 code safer (more like Py3) by preventing</span>
<span class="c"># implicit relative imports, you can also add this to the top:</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">absolute_import</span>
</pre></div>
</div>
</div>
<div class="section" id="dictionaries">
<h2>Dictionaries<a class="headerlink" href="#dictionaries" title="Permalink to this headline">¶</a></h2>
<div class="code python highlight-python"><div class="highlight"><pre><span class="n">heights</span> <span class="o">=</span> <span class="p">{</span><span class="s">&#39;Fred&#39;</span><span class="p">:</span> <span class="mi">175</span><span class="p">,</span> <span class="s">&#39;Anne&#39;</span><span class="p">:</span> <span class="mi">166</span><span class="p">,</span> <span class="s">&#39;Joe&#39;</span><span class="p">:</span> <span class="mi">192</span><span class="p">}</span>
</pre></div>
</div>
<div class="section" id="iterating-through-dict-keys-values-items">
<h3>Iterating through <code class="docutils literal"><span class="pre">dict</span></code> keys/values/items<a class="headerlink" href="#iterating-through-dict-keys-values-items" title="Permalink to this headline">¶</a></h3>
<p>Iterable dict keys:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">heights</span><span class="o">.</span><span class="n">iterkeys</span><span class="p">():</span>
    <span class="o">...</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">heights</span><span class="p">:</span>
    <span class="o">...</span>
</pre></div>
</div>
<p>Iterable dict values:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">for</span> <span class="n">value</span> <span class="ow">in</span> <span class="n">heights</span><span class="o">.</span><span class="n">itervalues</span><span class="p">():</span>
    <span class="o">...</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Idiomatic Python 3</span>
<span class="k">for</span> <span class="n">value</span> <span class="ow">in</span> <span class="n">heights</span><span class="o">.</span><span class="n">values</span><span class="p">():</span>    <span class="c"># extra memory overhead on Py2</span>
    <span class="o">...</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 1</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">dict</span>

<span class="n">heights</span> <span class="o">=</span> <span class="nb">dict</span><span class="p">(</span><span class="n">Fred</span><span class="o">=</span><span class="mi">175</span><span class="p">,</span> <span class="n">Anne</span><span class="o">=</span><span class="mi">166</span><span class="p">,</span> <span class="n">Joe</span><span class="o">=</span><span class="mi">192</span><span class="p">)</span>
<span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">heights</span><span class="o">.</span><span class="n">values</span><span class="p">():</span>    <span class="c"># efficient on Py2 and Py3</span>
    <span class="o">...</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 2</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="n">itervalues</span>
<span class="c"># or</span>
<span class="kn">from</span> <span class="nn">six</span> <span class="kn">import</span> <span class="n">itervalues</span>

<span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">itervalues</span><span class="p">(</span><span class="n">heights</span><span class="p">):</span>
    <span class="o">...</span>
</pre></div>
</div>
<p>Iterable dict items:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">for</span> <span class="p">(</span><span class="n">key</span><span class="p">,</span> <span class="n">value</span><span class="p">)</span> <span class="ow">in</span> <span class="n">heights</span><span class="o">.</span><span class="n">iteritems</span><span class="p">():</span>
    <span class="o">...</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 1</span>
<span class="k">for</span> <span class="p">(</span><span class="n">key</span><span class="p">,</span> <span class="n">value</span><span class="p">)</span> <span class="ow">in</span> <span class="n">heights</span><span class="o">.</span><span class="n">items</span><span class="p">():</span>    <span class="c"># inefficient on Py2</span>
    <span class="o">...</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 2</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">viewitems</span>

<span class="k">for</span> <span class="p">(</span><span class="n">key</span><span class="p">,</span> <span class="n">value</span><span class="p">)</span> <span class="ow">in</span> <span class="n">viewitems</span><span class="p">(</span><span class="n">heights</span><span class="p">):</span>   <span class="c"># also behaves like a set</span>
    <span class="o">...</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 3</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">iteritems</span>
<span class="c"># or</span>
<span class="kn">from</span> <span class="nn">six</span> <span class="kn">import</span> <span class="n">iteritems</span>

<span class="k">for</span> <span class="p">(</span><span class="n">key</span><span class="p">,</span> <span class="n">value</span><span class="p">)</span> <span class="ow">in</span> <span class="n">iteritems</span><span class="p">(</span><span class="n">heights</span><span class="p">):</span>
    <span class="o">...</span>
</pre></div>
</div>
</div>
<div class="section" id="dict-keys-values-items-as-a-list">
<h3>dict keys/values/items as a list<a class="headerlink" href="#dict-keys-values-items-as-a-list" title="Permalink to this headline">¶</a></h3>
<p>dict keys as a list:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="n">keylist</span> <span class="o">=</span> <span class="n">heights</span><span class="o">.</span><span class="n">keys</span><span class="p">()</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">keylist</span><span class="p">,</span> <span class="nb">list</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="n">keylist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">heights</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">keylist</span><span class="p">,</span> <span class="nb">list</span><span class="p">)</span>
</pre></div>
</div>
<p>dict values as a list:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="n">heights</span> <span class="o">=</span> <span class="p">{</span><span class="s">&#39;Fred&#39;</span><span class="p">:</span> <span class="mi">175</span><span class="p">,</span> <span class="s">&#39;Anne&#39;</span><span class="p">:</span> <span class="mi">166</span><span class="p">,</span> <span class="s">&#39;Joe&#39;</span><span class="p">:</span> <span class="mi">192</span><span class="p">}</span>
<span class="n">valuelist</span> <span class="o">=</span> <span class="n">heights</span><span class="o">.</span><span class="n">values</span><span class="p">()</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">valuelist</span><span class="p">,</span> <span class="nb">list</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 1</span>
<span class="n">valuelist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">heights</span><span class="o">.</span><span class="n">values</span><span class="p">())</span>    <span class="c"># inefficient on Py2</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 2</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">dict</span>

<span class="n">heights</span> <span class="o">=</span> <span class="nb">dict</span><span class="p">(</span><span class="n">Fred</span><span class="o">=</span><span class="mi">175</span><span class="p">,</span> <span class="n">Anne</span><span class="o">=</span><span class="mi">166</span><span class="p">,</span> <span class="n">Joe</span><span class="o">=</span><span class="mi">192</span><span class="p">)</span>
<span class="n">valuelist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">heights</span><span class="o">.</span><span class="n">values</span><span class="p">())</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 3</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">listvalues</span>

<span class="n">valuelist</span> <span class="o">=</span> <span class="n">listvalues</span><span class="p">(</span><span class="n">heights</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 4</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">itervalues</span>
<span class="c"># or</span>
<span class="kn">from</span> <span class="nn">six</span> <span class="kn">import</span> <span class="n">itervalues</span>

<span class="n">valuelist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">itervalues</span><span class="p">(</span><span class="n">heights</span><span class="p">))</span>
</pre></div>
</div>
<p>dict items as a list:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 1</span>
<span class="n">itemlist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">heights</span><span class="o">.</span><span class="n">items</span><span class="p">())</span>    <span class="c"># inefficient on Py2</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 2</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">listitems</span>

<span class="n">itemlist</span> <span class="o">=</span> <span class="n">listitems</span><span class="p">(</span><span class="n">heights</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 3</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">iteritems</span>
<span class="c"># or</span>
<span class="kn">from</span> <span class="nn">six</span> <span class="kn">import</span> <span class="n">iteritems</span>

<span class="n">itemlist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">iteritems</span><span class="p">(</span><span class="n">heights</span><span class="p">))</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="custom-class-behaviour">
<h2>Custom class behaviour<a class="headerlink" href="#custom-class-behaviour" title="Permalink to this headline">¶</a></h2>
<div class="section" id="custom-iterators">
<h3>Custom iterators<a class="headerlink" href="#custom-iterators" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only</span>
<span class="k">class</span> <span class="nc">Upper</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">iterable</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">_iter</span> <span class="o">=</span> <span class="nb">iter</span><span class="p">(</span><span class="n">iterable</span><span class="p">)</span>
    <span class="k">def</span> <span class="nf">next</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>          <span class="c"># Py2-style</span>
        <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_iter</span><span class="o">.</span><span class="n">next</span><span class="p">()</span><span class="o">.</span><span class="n">upper</span><span class="p">()</span>
    <span class="k">def</span> <span class="nf">__iter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="bp">self</span>

<span class="n">itr</span> <span class="o">=</span> <span class="n">Upper</span><span class="p">(</span><span class="s">&#39;hello&#39;</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">itr</span><span class="o">.</span><span class="n">next</span><span class="p">()</span> <span class="o">==</span> <span class="s">&#39;H&#39;</span>     <span class="c"># Py2-style</span>
<span class="k">assert</span> <span class="nb">list</span><span class="p">(</span><span class="n">itr</span><span class="p">)</span> <span class="o">==</span> <span class="nb">list</span><span class="p">(</span><span class="s">&#39;ELLO&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 1</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">object</span>

<span class="k">class</span> <span class="nc">Upper</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">iterable</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">_iter</span> <span class="o">=</span> <span class="nb">iter</span><span class="p">(</span><span class="n">iterable</span><span class="p">)</span>
    <span class="k">def</span> <span class="nf">__next__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>      <span class="c"># Py3-style iterator interface</span>
        <span class="k">return</span> <span class="nb">next</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_iter</span><span class="p">)</span><span class="o">.</span><span class="n">upper</span><span class="p">()</span>  <span class="c"># builtin next() function calls</span>
    <span class="k">def</span> <span class="nf">__iter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="bp">self</span>

<span class="n">itr</span> <span class="o">=</span> <span class="n">Upper</span><span class="p">(</span><span class="s">&#39;hello&#39;</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">next</span><span class="p">(</span><span class="n">itr</span><span class="p">)</span> <span class="o">==</span> <span class="s">&#39;H&#39;</span>      <span class="c"># compatible style</span>
<span class="k">assert</span> <span class="nb">list</span><span class="p">(</span><span class="n">itr</span><span class="p">)</span> <span class="o">==</span> <span class="nb">list</span><span class="p">(</span><span class="s">&#39;ELLO&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 2</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">implements_iterator</span>

<span class="nd">@implements_iterator</span>
<span class="k">class</span> <span class="nc">Upper</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">iterable</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">_iter</span> <span class="o">=</span> <span class="nb">iter</span><span class="p">(</span><span class="n">iterable</span><span class="p">)</span>
    <span class="k">def</span> <span class="nf">__next__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>                  <span class="c"># Py3-style iterator interface</span>
        <span class="k">return</span> <span class="nb">next</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_iter</span><span class="p">)</span><span class="o">.</span><span class="n">upper</span><span class="p">()</span>  <span class="c"># builtin next() function calls</span>
    <span class="k">def</span> <span class="nf">__iter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="bp">self</span>

<span class="n">itr</span> <span class="o">=</span> <span class="n">Upper</span><span class="p">(</span><span class="s">&#39;hello&#39;</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">next</span><span class="p">(</span><span class="n">itr</span><span class="p">)</span> <span class="o">==</span> <span class="s">&#39;H&#39;</span>
<span class="k">assert</span> <span class="nb">list</span><span class="p">(</span><span class="n">itr</span><span class="p">)</span> <span class="o">==</span> <span class="nb">list</span><span class="p">(</span><span class="s">&#39;ELLO&#39;</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="custom-str-methods">
<h3>Custom <code class="docutils literal"><span class="pre">__str__</span></code> methods<a class="headerlink" href="#custom-str-methods" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">class</span> <span class="nc">MyClass</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">__unicode__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="s">&#39;Unicode string: </span><span class="se">\u5b54\u5b50</span><span class="s">&#39;</span>
    <span class="k">def</span> <span class="nf">__str__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="nb">unicode</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s">&#39;utf-8&#39;</span><span class="p">)</span>

<span class="n">a</span> <span class="o">=</span> <span class="n">MyClass</span><span class="p">()</span>
<span class="k">print</span><span class="p">(</span><span class="n">a</span><span class="p">)</span>    <span class="c"># prints encoded string</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">python_2_unicode_compatible</span>

<span class="nd">@python_2_unicode_compatible</span>
<span class="k">class</span> <span class="nc">MyClass</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">__str__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="s">u&#39;Unicode string: </span><span class="se">\u5b54\u5b50</span><span class="s">&#39;</span>

<span class="n">a</span> <span class="o">=</span> <span class="n">MyClass</span><span class="p">()</span>
<span class="k">print</span><span class="p">(</span><span class="n">a</span><span class="p">)</span>    <span class="c"># prints string encoded as utf-8 on Py2</span>
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre>Unicode string: 孔子
</pre></div>
</div>
</div>
<div class="section" id="custom-nonzero-vs-bool-method">
<h3>Custom <code class="docutils literal"><span class="pre">__nonzero__</span></code> vs <code class="docutils literal"><span class="pre">__bool__</span></code> method:<a class="headerlink" href="#custom-nonzero-vs-bool-method" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">class</span> <span class="nc">AllOrNothing</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">l</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">l</span> <span class="o">=</span> <span class="n">l</span>
    <span class="k">def</span> <span class="nf">__nonzero__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="nb">all</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">l</span><span class="p">)</span>

<span class="n">container</span> <span class="o">=</span> <span class="n">AllOrNothing</span><span class="p">([</span><span class="mi">0</span><span class="p">,</span> <span class="mi">100</span><span class="p">,</span> <span class="mi">200</span><span class="p">])</span>
<span class="k">assert</span> <span class="ow">not</span> <span class="nb">bool</span><span class="p">(</span><span class="n">container</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">object</span>

<span class="k">class</span> <span class="nc">AllOrNothing</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">l</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">l</span> <span class="o">=</span> <span class="n">l</span>
    <span class="k">def</span> <span class="nf">__bool__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="nb">all</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">l</span><span class="p">)</span>

<span class="n">container</span> <span class="o">=</span> <span class="n">AllOrNothing</span><span class="p">([</span><span class="mi">0</span><span class="p">,</span> <span class="mi">100</span><span class="p">,</span> <span class="mi">200</span><span class="p">])</span>
<span class="k">assert</span> <span class="ow">not</span> <span class="nb">bool</span><span class="p">(</span><span class="n">container</span><span class="p">)</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="lists-versus-iterators">
<h2>Lists versus iterators<a class="headerlink" href="#lists-versus-iterators" title="Permalink to this headline">¶</a></h2>
<div class="section" id="xrange">
<h3>xrange<a class="headerlink" href="#xrange" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">xrange</span><span class="p">(</span><span class="mi">10</span><span class="o">**</span><span class="mi">8</span><span class="p">):</span>
    <span class="o">...</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: forward-compatible</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">range</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="o">**</span><span class="mi">8</span><span class="p">):</span>
    <span class="o">...</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: backward-compatible</span>
<span class="kn">from</span> <span class="nn">past.builtins</span> <span class="kn">import</span> <span class="nb">xrange</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">xrange</span><span class="p">(</span><span class="mi">10</span><span class="o">**</span><span class="mi">8</span><span class="p">):</span>
    <span class="o">...</span>
</pre></div>
</div>
</div>
<div class="section" id="range">
<h3>range<a class="headerlink" href="#range" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only</span>
<span class="n">mylist</span> <span class="o">=</span> <span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">mylist</span> <span class="o">==</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: forward-compatible: option 1</span>
<span class="n">mylist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">))</span>            <span class="c"># copies memory on Py2</span>
<span class="k">assert</span> <span class="n">mylist</span> <span class="o">==</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: forward-compatible: option 2</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">range</span>

<span class="n">mylist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">))</span>
<span class="k">assert</span> <span class="n">mylist</span> <span class="o">==</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 3</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">lrange</span>

<span class="n">mylist</span> <span class="o">=</span> <span class="n">lrange</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">mylist</span> <span class="o">==</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: backward compatible</span>
<span class="kn">from</span> <span class="nn">past.builtins</span> <span class="kn">import</span> <span class="nb">range</span>

<span class="n">mylist</span> <span class="o">=</span> <span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">mylist</span> <span class="o">==</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="section" id="map">
<h3>map<a class="headerlink" href="#map" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="n">mynewlist</span> <span class="o">=</span> <span class="nb">map</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">myoldlist</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">mynewlist</span> <span class="o">==</span> <span class="p">[</span><span class="n">f</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">myoldlist</span><span class="p">]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 1</span>
<span class="c"># Idiomatic Py3, but inefficient on Py2</span>
<span class="n">mynewlist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="nb">map</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">myoldlist</span><span class="p">))</span>
<span class="k">assert</span> <span class="n">mynewlist</span> <span class="o">==</span> <span class="p">[</span><span class="n">f</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">myoldlist</span><span class="p">]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 2</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">map</span>

<span class="n">mynewlist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="nb">map</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">myoldlist</span><span class="p">))</span>
<span class="k">assert</span> <span class="n">mynewlist</span> <span class="o">==</span> <span class="p">[</span><span class="n">f</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">myoldlist</span><span class="p">]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 3</span>
<span class="k">try</span><span class="p">:</span>
    <span class="kn">import</span> <span class="nn">itertools.imap</span> <span class="kn">as</span> <span class="nn">map</span>
<span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span>
    <span class="k">pass</span>

<span class="n">mynewlist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="nb">map</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">myoldlist</span><span class="p">))</span>    <span class="c"># inefficient on Py2</span>
<span class="k">assert</span> <span class="n">mynewlist</span> <span class="o">==</span> <span class="p">[</span><span class="n">f</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">myoldlist</span><span class="p">]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 4</span>
<span class="kn">from</span> <span class="nn">future.utils</span> <span class="kn">import</span> <span class="n">lmap</span>

<span class="n">mynewlist</span> <span class="o">=</span> <span class="n">lmap</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">myoldlist</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">mynewlist</span> <span class="o">==</span> <span class="p">[</span><span class="n">f</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">myoldlist</span><span class="p">]</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 5</span>
<span class="kn">from</span> <span class="nn">past.builtins</span> <span class="kn">import</span> <span class="nb">map</span>

<span class="n">mynewlist</span> <span class="o">=</span> <span class="nb">map</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">myoldlist</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">mynewlist</span> <span class="o">==</span> <span class="p">[</span><span class="n">f</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">myoldlist</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="section" id="imap">
<h3>imap<a class="headerlink" href="#imap" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">from</span> <span class="nn">itertools</span> <span class="kn">import</span> <span class="n">imap</span>

<span class="n">myiter</span> <span class="o">=</span> <span class="n">imap</span><span class="p">(</span><span class="n">func</span><span class="p">,</span> <span class="n">myoldlist</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">myiter</span><span class="p">,</span> <span class="nb">iter</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only:</span>
<span class="n">myiter</span> <span class="o">=</span> <span class="nb">map</span><span class="p">(</span><span class="n">func</span><span class="p">,</span> <span class="n">myoldlist</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">myiter</span><span class="p">,</span> <span class="nb">iter</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 1</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">map</span>

<span class="n">myiter</span> <span class="o">=</span> <span class="nb">map</span><span class="p">(</span><span class="n">func</span><span class="p">,</span> <span class="n">myoldlist</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">myiter</span><span class="p">,</span> <span class="nb">iter</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 2</span>
<span class="k">try</span><span class="p">:</span>
    <span class="kn">import</span> <span class="nn">itertools.imap</span> <span class="kn">as</span> <span class="nn">map</span>
<span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span>
    <span class="k">pass</span>

<span class="n">myiter</span> <span class="o">=</span> <span class="nb">map</span><span class="p">(</span><span class="n">func</span><span class="p">,</span> <span class="n">myoldlist</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">myiter</span><span class="p">,</span> <span class="nb">iter</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="zip-izip">
<h3>zip, izip<a class="headerlink" href="#zip-izip" title="Permalink to this headline">¶</a></h3>
<p>As above with <code class="docutils literal"><span class="pre">zip</span></code> and <code class="docutils literal"><span class="pre">itertools.izip</span></code>.</p>
</div>
<div class="section" id="filter-ifilter">
<h3>filter, ifilter<a class="headerlink" href="#filter-ifilter" title="Permalink to this headline">¶</a></h3>
<p>As above with <code class="docutils literal"><span class="pre">filter</span></code> and <code class="docutils literal"><span class="pre">itertools.ifilter</span></code> too.</p>
</div>
</div>
<div class="section" id="other-builtins">
<h2>Other builtins<a class="headerlink" href="#other-builtins" title="Permalink to this headline">¶</a></h2>
<div class="section" id="file-io-with-open">
<h3>File IO with open()<a class="headerlink" href="#file-io-with-open" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only</span>
<span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s">&#39;myfile.txt&#39;</span><span class="p">)</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>              <span class="c"># as a byte string</span>
<span class="n">text</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s">&#39;utf-8&#39;</span><span class="p">)</span>

<span class="c"># Python 2 and 3: alternative 1</span>
<span class="kn">from</span> <span class="nn">io</span> <span class="kn">import</span> <span class="nb">open</span>
<span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s">&#39;myfile.txt&#39;</span><span class="p">,</span> <span class="s">&#39;rb&#39;</span><span class="p">)</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>              <span class="c"># as bytes</span>
<span class="n">text</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s">&#39;utf-8&#39;</span><span class="p">)</span>  <span class="c"># unicode, not bytes</span>

<span class="c"># Python 2 and 3: alternative 2</span>
<span class="kn">from</span> <span class="nn">io</span> <span class="kn">import</span> <span class="nb">open</span>
<span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s">&#39;myfile.txt&#39;</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="s">&#39;utf-8&#39;</span><span class="p">)</span>
<span class="n">text</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>    <span class="c"># unicode, not bytes</span>
</pre></div>
</div>
</div>
<div class="section" id="reduce">
<h3>reduce()<a class="headerlink" href="#reduce" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">assert</span> <span class="nb">reduce</span><span class="p">(</span><span class="k">lambda</span> <span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">:</span> <span class="n">x</span><span class="o">+</span><span class="n">y</span><span class="p">,</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="o">==</span> <span class="mi">1</span><span class="o">+</span><span class="mi">2</span><span class="o">+</span><span class="mi">3</span><span class="o">+</span><span class="mi">4</span><span class="o">+</span><span class="mi">5</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">functools</span> <span class="kn">import</span> <span class="nb">reduce</span>

<span class="k">assert</span> <span class="nb">reduce</span><span class="p">(</span><span class="k">lambda</span> <span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">:</span> <span class="n">x</span><span class="o">+</span><span class="n">y</span><span class="p">,</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="o">==</span> <span class="mi">1</span><span class="o">+</span><span class="mi">2</span><span class="o">+</span><span class="mi">3</span><span class="o">+</span><span class="mi">4</span><span class="o">+</span><span class="mi">5</span>
</pre></div>
</div>
</div>
<div class="section" id="raw-input">
<h3>raw_input()<a class="headerlink" href="#raw-input" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="n">name</span> <span class="o">=</span> <span class="nb">raw_input</span><span class="p">(</span><span class="s">&#39;What is your name? &#39;</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="nb">str</span><span class="p">)</span>    <span class="c"># native str</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">input</span>

<span class="n">name</span> <span class="o">=</span> <span class="nb">input</span><span class="p">(</span><span class="s">&#39;What is your name? &#39;</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="nb">str</span><span class="p">)</span>    <span class="c"># native str on Py2 and Py3</span>
</pre></div>
</div>
</div>
<div class="section" id="input">
<h3>input()<a class="headerlink" href="#input" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="nb">input</span><span class="p">(</span><span class="s">&quot;Type something safe please: &quot;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">input</span>
<span class="nb">eval</span><span class="p">(</span><span class="nb">input</span><span class="p">(</span><span class="s">&quot;Type something safe please: &quot;</span><span class="p">))</span>
</pre></div>
</div>
<p>Warning: using either of these is <strong>unsafe</strong> with untrusted input.</p>
</div>
<div class="section" id="file">
<h3>file()<a class="headerlink" href="#file" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="n">f</span> <span class="o">=</span> <span class="nb">file</span><span class="p">(</span><span class="n">pathname</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">pathname</span><span class="p">)</span>

<span class="c"># But preferably, use this:</span>
<span class="kn">from</span> <span class="nn">io</span> <span class="kn">import</span> <span class="nb">open</span>
<span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">pathname</span><span class="p">,</span> <span class="s">&#39;rb&#39;</span><span class="p">)</span>   <span class="c"># if f.read() should return bytes</span>
<span class="c"># or</span>
<span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">pathname</span><span class="p">,</span> <span class="s">&#39;rt&#39;</span><span class="p">)</span>   <span class="c"># if f.read() should return unicode text</span>
</pre></div>
</div>
</div>
<div class="section" id="execfile">
<h3>execfile()<a class="headerlink" href="#execfile" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="nb">execfile</span><span class="p">(</span><span class="s">&#39;myfile.py&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 1</span>
<span class="kn">from</span> <span class="nn">past.builtins</span> <span class="kn">import</span> <span class="nb">execfile</span>

<span class="nb">execfile</span><span class="p">(</span><span class="s">&#39;myfile.py&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 2</span>
<span class="k">exec</span><span class="p">(</span><span class="nb">compile</span><span class="p">(</span><span class="nb">open</span><span class="p">(</span><span class="s">&#39;myfile.py&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">read</span><span class="p">()))</span>

<span class="c"># This can sometimes cause this:</span>
<span class="c">#     SyntaxError: function ... uses import * and bare exec ...</span>
<span class="c"># See https://github.com/PythonCharmers/python-future/issues/37</span>
</pre></div>
</div>
</div>
<div class="section" id="unichr">
<h3>unichr()<a class="headerlink" href="#unichr" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">assert</span> <span class="nb">unichr</span><span class="p">(</span><span class="mi">8364</span><span class="p">)</span> <span class="o">==</span> <span class="s">&#39;€&#39;</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only:</span>
<span class="k">assert</span> <span class="nb">chr</span><span class="p">(</span><span class="mi">8364</span><span class="p">)</span> <span class="o">==</span> <span class="s">&#39;€&#39;</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">chr</span>
<span class="k">assert</span> <span class="nb">chr</span><span class="p">(</span><span class="mi">8364</span><span class="p">)</span> <span class="o">==</span> <span class="s">&#39;€&#39;</span>
</pre></div>
</div>
</div>
<div class="section" id="intern">
<h3>intern()<a class="headerlink" href="#intern" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="nb">intern</span><span class="p">(</span><span class="s">&#39;mystring&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only:</span>
<span class="kn">from</span> <span class="nn">sys</span> <span class="kn">import</span> <span class="nb">intern</span>
<span class="nb">intern</span><span class="p">(</span><span class="s">&#39;mystring&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 1</span>
<span class="kn">from</span> <span class="nn">past.builtins</span> <span class="kn">import</span> <span class="nb">intern</span>
<span class="nb">intern</span><span class="p">(</span><span class="s">&#39;mystring&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 2</span>
<span class="kn">from</span> <span class="nn">six.moves</span> <span class="kn">import</span> <span class="nb">intern</span>
<span class="nb">intern</span><span class="p">(</span><span class="s">&#39;mystring&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 3</span>
<span class="kn">from</span> <span class="nn">future.standard_library</span> <span class="kn">import</span> <span class="n">install_aliases</span>
<span class="n">install_aliases</span><span class="p">()</span>
<span class="kn">from</span> <span class="nn">sys</span> <span class="kn">import</span> <span class="nb">intern</span>
<span class="nb">intern</span><span class="p">(</span><span class="s">&#39;mystring&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 2</span>
<span class="k">try</span><span class="p">:</span>
    <span class="kn">from</span> <span class="nn">sys</span> <span class="kn">import</span> <span class="nb">intern</span>
<span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span>
    <span class="k">pass</span>
<span class="nb">intern</span><span class="p">(</span><span class="s">&#39;mystring&#39;</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="apply">
<h3>apply()<a class="headerlink" href="#apply" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="n">args</span> <span class="o">=</span> <span class="p">(</span><span class="s">&#39;a&#39;</span><span class="p">,</span> <span class="s">&#39;b&#39;</span><span class="p">)</span>
<span class="n">kwargs</span> <span class="o">=</span> <span class="p">{</span><span class="s">&#39;kwarg1&#39;</span><span class="p">:</span> <span class="bp">True</span><span class="p">}</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="nb">apply</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">args</span><span class="p">,</span> <span class="n">kwargs</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 1</span>
<span class="n">f</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 2</span>
<span class="kn">from</span> <span class="nn">past.builtins</span> <span class="kn">import</span> <span class="nb">apply</span>
<span class="nb">apply</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">args</span><span class="p">,</span> <span class="n">kwargs</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="chr">
<h3>chr()<a class="headerlink" href="#chr" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">assert</span> <span class="nb">chr</span><span class="p">(</span><span class="mi">64</span><span class="p">)</span> <span class="o">==</span> <span class="n">b</span><span class="s">&#39;@&#39;</span>
<span class="k">assert</span> <span class="nb">chr</span><span class="p">(</span><span class="mi">200</span><span class="p">)</span> <span class="o">==</span> <span class="n">b</span><span class="s">&#39;</span><span class="se">\xc8</span><span class="s">&#39;</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only: option 1</span>
<span class="k">assert</span> <span class="nb">chr</span><span class="p">(</span><span class="mi">64</span><span class="p">)</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s">&#39;latin-1&#39;</span><span class="p">)</span> <span class="o">==</span> <span class="n">b</span><span class="s">&#39;@&#39;</span>
<span class="k">assert</span> <span class="nb">chr</span><span class="p">(</span><span class="mh">0xc8</span><span class="p">)</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s">&#39;latin-1&#39;</span><span class="p">)</span> <span class="o">==</span> <span class="n">b</span><span class="s">&#39;</span><span class="se">\xc8</span><span class="s">&#39;</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 1</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">chr</span>

<span class="k">assert</span> <span class="nb">chr</span><span class="p">(</span><span class="mi">64</span><span class="p">)</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s">&#39;latin-1&#39;</span><span class="p">)</span> <span class="o">==</span> <span class="n">b</span><span class="s">&#39;@&#39;</span>
<span class="k">assert</span> <span class="nb">chr</span><span class="p">(</span><span class="mh">0xc8</span><span class="p">)</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s">&#39;latin-1&#39;</span><span class="p">)</span> <span class="o">==</span> <span class="n">b</span><span class="s">&#39;</span><span class="se">\xc8</span><span class="s">&#39;</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only: option 2</span>
<span class="k">assert</span> <span class="nb">bytes</span><span class="p">([</span><span class="mi">64</span><span class="p">])</span> <span class="o">==</span> <span class="n">b</span><span class="s">&#39;@&#39;</span>
<span class="k">assert</span> <span class="nb">bytes</span><span class="p">([</span><span class="mh">0xc8</span><span class="p">])</span> <span class="o">==</span> <span class="n">b</span><span class="s">&#39;</span><span class="se">\xc8</span><span class="s">&#39;</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: option 2</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">bytes</span>

<span class="k">assert</span> <span class="nb">bytes</span><span class="p">([</span><span class="mi">64</span><span class="p">])</span> <span class="o">==</span> <span class="n">b</span><span class="s">&#39;@&#39;</span>
<span class="k">assert</span> <span class="nb">bytes</span><span class="p">([</span><span class="mh">0xc8</span><span class="p">])</span> <span class="o">==</span> <span class="n">b</span><span class="s">&#39;</span><span class="se">\xc8</span><span class="s">&#39;</span>
</pre></div>
</div>
</div>
<div class="section" id="cmp">
<h3>cmp()<a class="headerlink" href="#cmp" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="k">assert</span> <span class="nb">cmp</span><span class="p">(</span><span class="s">&#39;a&#39;</span><span class="p">,</span> <span class="s">&#39;b&#39;</span><span class="p">)</span> <span class="o">&lt;</span> <span class="mi">0</span> <span class="ow">and</span> <span class="nb">cmp</span><span class="p">(</span><span class="s">&#39;b&#39;</span><span class="p">,</span> <span class="s">&#39;a&#39;</span><span class="p">)</span> <span class="o">&gt;</span> <span class="mi">0</span> <span class="ow">and</span> <span class="nb">cmp</span><span class="p">(</span><span class="s">&#39;c&#39;</span><span class="p">,</span> <span class="s">&#39;c&#39;</span><span class="p">)</span> <span class="o">==</span> <span class="mi">0</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 1</span>
<span class="kn">from</span> <span class="nn">past.builtins</span> <span class="kn">import</span> <span class="nb">cmp</span>
<span class="k">assert</span> <span class="nb">cmp</span><span class="p">(</span><span class="s">&#39;a&#39;</span><span class="p">,</span> <span class="s">&#39;b&#39;</span><span class="p">)</span> <span class="o">&lt;</span> <span class="mi">0</span> <span class="ow">and</span> <span class="nb">cmp</span><span class="p">(</span><span class="s">&#39;b&#39;</span><span class="p">,</span> <span class="s">&#39;a&#39;</span><span class="p">)</span> <span class="o">&gt;</span> <span class="mi">0</span> <span class="ow">and</span> <span class="nb">cmp</span><span class="p">(</span><span class="s">&#39;c&#39;</span><span class="p">,</span> <span class="s">&#39;c&#39;</span><span class="p">)</span> <span class="o">==</span> <span class="mi">0</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre># Python 2 and 3: alternative 2
cmp = lambda(x, y): (x &gt; y) - (x &lt; y)
assert cmp(&#39;a&#39;, &#39;b&#39;) &lt; 0 and cmp(&#39;b&#39;, &#39;a&#39;) &gt; 0 and cmp(&#39;c&#39;, &#39;c&#39;) == 0
</pre></div>
</div>
</div>
<div class="section" id="reload">
<h3>reload()<a class="headerlink" href="#reload" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="nb">reload</span><span class="p">(</span><span class="n">mymodule</span><span class="p">)</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3</span>
<span class="kn">from</span> <span class="nn">imp</span> <span class="kn">import</span> <span class="nb">reload</span>
<span class="nb">reload</span><span class="p">(</span><span class="n">mymodule</span><span class="p">)</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="standard-library">
<h2>Standard library<a class="headerlink" href="#standard-library" title="Permalink to this headline">¶</a></h2>
<div class="section" id="dbm-modules">
<h3>dbm modules<a class="headerlink" href="#dbm-modules" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only</span>
<span class="kn">import</span> <span class="nn">anydbm</span>
<span class="kn">import</span> <span class="nn">whichdb</span>
<span class="kn">import</span> <span class="nn">dbm</span>
<span class="kn">import</span> <span class="nn">dumbdbm</span>
<span class="kn">import</span> <span class="nn">gdbm</span>

<span class="c"># Python 2 and 3: alternative 1</span>
<span class="kn">from</span> <span class="nn">future</span> <span class="kn">import</span> <span class="n">standard_library</span>
<span class="n">standard_library</span><span class="o">.</span><span class="n">install_aliases</span><span class="p">()</span>

<span class="kn">import</span> <span class="nn">dbm</span>
<span class="kn">import</span> <span class="nn">dbm.ndbm</span>
<span class="kn">import</span> <span class="nn">dbm.dumb</span>
<span class="kn">import</span> <span class="nn">dbm.gnu</span>

<span class="c"># Python 2 and 3: alternative 2</span>
<span class="kn">from</span> <span class="nn">future.moves</span> <span class="kn">import</span> <span class="n">dbm</span>
<span class="kn">from</span> <span class="nn">future.moves.dbm</span> <span class="kn">import</span> <span class="n">dumb</span>
<span class="kn">from</span> <span class="nn">future.moves.dbm</span> <span class="kn">import</span> <span class="n">ndbm</span>
<span class="kn">from</span> <span class="nn">future.moves.dbm</span> <span class="kn">import</span> <span class="n">gnu</span>

<span class="c"># Python 2 and 3: alternative 3</span>
<span class="kn">from</span> <span class="nn">six.moves</span> <span class="kn">import</span> <span class="n">dbm_gnu</span>
<span class="c"># (others not supported)</span>
</pre></div>
</div>
</div>
<div class="section" id="commands-subprocess-modules">
<h3>commands / subprocess modules<a class="headerlink" href="#commands-subprocess-modules" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only</span>
<span class="kn">from</span> <span class="nn">commands</span> <span class="kn">import</span> <span class="n">getoutput</span><span class="p">,</span> <span class="n">getstatusoutput</span>

<span class="c"># Python 2 and 3</span>
<span class="kn">from</span> <span class="nn">future</span> <span class="kn">import</span> <span class="n">standard_library</span>
<span class="n">standard_library</span><span class="o">.</span><span class="n">install_aliases</span><span class="p">()</span>

<span class="kn">from</span> <span class="nn">subprocess</span> <span class="kn">import</span> <span class="n">getoutput</span><span class="p">,</span> <span class="n">getstatusoutput</span>
</pre></div>
</div>
</div>
<div class="section" id="subprocess-check-output">
<h3>subprocess.check_output()<a class="headerlink" href="#subprocess-check-output" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2.7 and above</span>
<span class="kn">from</span> <span class="nn">subprocess</span> <span class="kn">import</span> <span class="n">check_output</span>

<span class="c"># Python 2.6 and above: alternative 1</span>
<span class="kn">from</span> <span class="nn">future.moves.subprocess</span> <span class="kn">import</span> <span class="n">check_output</span>

<span class="c"># Python 2.6 and above: alternative 2</span>
<span class="kn">from</span> <span class="nn">future</span> <span class="kn">import</span> <span class="n">standard_library</span>
<span class="n">standard_library</span><span class="o">.</span><span class="n">install_aliases</span><span class="p">()</span>

<span class="kn">from</span> <span class="nn">subprocess</span> <span class="kn">import</span> <span class="n">check_output</span>
</pre></div>
</div>
</div>
<div class="section" id="collections-counter-and-ordereddict">
<h3>collections: Counter and OrderedDict<a class="headerlink" href="#collections-counter-and-ordereddict" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2.7 and above</span>
<span class="kn">from</span> <span class="nn">collections</span> <span class="kn">import</span> <span class="n">Counter</span><span class="p">,</span> <span class="n">OrderedDict</span>

<span class="c"># Python 2.6 and above: alternative 1</span>
<span class="kn">from</span> <span class="nn">future.moves.collections</span> <span class="kn">import</span> <span class="n">Counter</span><span class="p">,</span> <span class="n">OrderedDict</span>

<span class="c"># Python 2.6 and above: alternative 2</span>
<span class="kn">from</span> <span class="nn">future</span> <span class="kn">import</span> <span class="n">standard_library</span>
<span class="n">standard_library</span><span class="o">.</span><span class="n">install_aliases</span><span class="p">()</span>

<span class="kn">from</span> <span class="nn">collections</span> <span class="kn">import</span> <span class="n">Counter</span><span class="p">,</span> <span class="n">OrderedDict</span>
</pre></div>
</div>
</div>
<div class="section" id="stringio-module">
<h3>StringIO module<a class="headerlink" href="#stringio-module" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only</span>
<span class="kn">from</span> <span class="nn">StringIO</span> <span class="kn">import</span> <span class="n">StringIO</span>
<span class="kn">from</span> <span class="nn">cStringIO</span> <span class="kn">import</span> <span class="n">StringIO</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3</span>
<span class="kn">from</span> <span class="nn">io</span> <span class="kn">import</span> <span class="n">BytesIO</span>
<span class="c"># and refactor StringIO() calls to BytesIO() if passing byte-strings</span>
</pre></div>
</div>
</div>
<div class="section" id="http-module">
<h3>http module<a class="headerlink" href="#http-module" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">import</span> <span class="nn">httplib</span>
<span class="kn">import</span> <span class="nn">Cookie</span>
<span class="kn">import</span> <span class="nn">cookielib</span>
<span class="kn">import</span> <span class="nn">BaseHTTPServer</span>
<span class="kn">import</span> <span class="nn">SimpleHTTPServer</span>
<span class="kn">import</span> <span class="nn">CGIHttpServer</span>

<span class="c"># Python 2 and 3 (after ``pip install future``):</span>
<span class="kn">import</span> <span class="nn">http.client</span>
<span class="kn">import</span> <span class="nn">http.cookies</span>
<span class="kn">import</span> <span class="nn">http.cookiejar</span>
<span class="kn">import</span> <span class="nn">http.server</span>
</pre></div>
</div>
</div>
<div class="section" id="xmlrpc-module">
<h3>xmlrpc module<a class="headerlink" href="#xmlrpc-module" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">import</span> <span class="nn">DocXMLRPCServer</span>
<span class="kn">import</span> <span class="nn">SimpleXMLRPCServer</span>

<span class="c"># Python 2 and 3 (after ``pip install future``):</span>
<span class="kn">import</span> <span class="nn">xmlrpc.server</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">import</span> <span class="nn">xmlrpclib</span>

<span class="c"># Python 2 and 3 (after ``pip install future``):</span>
<span class="kn">import</span> <span class="nn">xmlrpc.client</span>
</pre></div>
</div>
</div>
<div class="section" id="html-escaping-and-entities">
<h3>html escaping and entities<a class="headerlink" href="#html-escaping-and-entities" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3:</span>
<span class="kn">from</span> <span class="nn">cgi</span> <span class="kn">import</span> <span class="n">escape</span>

<span class="c"># Safer (Python 2 and 3, after ``pip install future``):</span>
<span class="kn">from</span> <span class="nn">html</span> <span class="kn">import</span> <span class="n">escape</span>

<span class="c"># Python 2 only:</span>
<span class="kn">from</span> <span class="nn">htmlentitydefs</span> <span class="kn">import</span> <span class="n">codepoint2name</span><span class="p">,</span> <span class="n">entitydefs</span><span class="p">,</span> <span class="n">name2codepoint</span>

<span class="c"># Python 2 and 3 (after ``pip install future``):</span>
<span class="kn">from</span> <span class="nn">html.entities</span> <span class="kn">import</span> <span class="n">codepoint2name</span><span class="p">,</span> <span class="n">entitydefs</span><span class="p">,</span> <span class="n">name2codepoint</span>
</pre></div>
</div>
</div>
<div class="section" id="html-parsing">
<h3>html parsing<a class="headerlink" href="#html-parsing" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">from</span> <span class="nn">HTMLParser</span> <span class="kn">import</span> <span class="n">HTMLParser</span>

<span class="c"># Python 2 and 3 (after ``pip install future``)</span>
<span class="kn">from</span> <span class="nn">html.parser</span> <span class="kn">import</span> <span class="n">HTMLParser</span>

<span class="c"># Python 2 and 3 (alternative 2):</span>
<span class="kn">from</span> <span class="nn">future.moves.html.parser</span> <span class="kn">import</span> <span class="n">HTMLParser</span>
</pre></div>
</div>
</div>
<div class="section" id="urllib-module">
<h3>urllib module<a class="headerlink" href="#urllib-module" title="Permalink to this headline">¶</a></h3>
<p><code class="docutils literal"><span class="pre">urllib</span></code> is the hardest module to use from Python 2/3 compatible code.
You may like to use Requests (<a class="reference external" href="http://python-requests.org">http://python-requests.org</a>) instead.</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">from</span> <span class="nn">urlparse</span> <span class="kn">import</span> <span class="n">urlparse</span>
<span class="kn">from</span> <span class="nn">urllib</span> <span class="kn">import</span> <span class="n">urlencode</span>
<span class="kn">from</span> <span class="nn">urllib2</span> <span class="kn">import</span> <span class="n">urlopen</span><span class="p">,</span> <span class="n">Request</span><span class="p">,</span> <span class="n">HTTPError</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 3 only:</span>
<span class="kn">from</span> <span class="nn">urllib.parse</span> <span class="kn">import</span> <span class="n">urlparse</span><span class="p">,</span> <span class="n">urlencode</span>
<span class="kn">from</span> <span class="nn">urllib.request</span> <span class="kn">import</span> <span class="n">urlopen</span><span class="p">,</span> <span class="n">Request</span>
<span class="kn">from</span> <span class="nn">urllib.error</span> <span class="kn">import</span> <span class="n">HTTPError</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: easiest option</span>
<span class="kn">from</span> <span class="nn">future.standard_library</span> <span class="kn">import</span> <span class="n">install_aliases</span>
<span class="n">install_aliases</span><span class="p">()</span>

<span class="kn">from</span> <span class="nn">urllib.parse</span> <span class="kn">import</span> <span class="n">urlparse</span><span class="p">,</span> <span class="n">urlencode</span>
<span class="kn">from</span> <span class="nn">urllib.request</span> <span class="kn">import</span> <span class="n">urlopen</span><span class="p">,</span> <span class="n">Request</span>
<span class="kn">from</span> <span class="nn">urllib.error</span> <span class="kn">import</span> <span class="n">HTTPError</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 2</span>
<span class="kn">from</span> <span class="nn">future.standard_library</span> <span class="kn">import</span> <span class="n">hooks</span>

<span class="k">with</span> <span class="n">hooks</span><span class="p">():</span>
    <span class="kn">from</span> <span class="nn">urllib.parse</span> <span class="kn">import</span> <span class="n">urlparse</span><span class="p">,</span> <span class="n">urlencode</span>
    <span class="kn">from</span> <span class="nn">urllib.request</span> <span class="kn">import</span> <span class="n">urlopen</span><span class="p">,</span> <span class="n">Request</span>
    <span class="kn">from</span> <span class="nn">urllib.error</span> <span class="kn">import</span> <span class="n">HTTPError</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 3</span>
<span class="kn">from</span> <span class="nn">future.moves.urllib.parse</span> <span class="kn">import</span> <span class="n">urlparse</span><span class="p">,</span> <span class="n">urlencode</span>
<span class="kn">from</span> <span class="nn">future.moves.urllib.request</span> <span class="kn">import</span> <span class="n">urlopen</span><span class="p">,</span> <span class="n">Request</span>
<span class="kn">from</span> <span class="nn">future.moves.urllib.error</span> <span class="kn">import</span> <span class="n">HTTPError</span>
<span class="c"># or</span>
<span class="kn">from</span> <span class="nn">six.moves.urllib.parse</span> <span class="kn">import</span> <span class="n">urlparse</span><span class="p">,</span> <span class="n">urlencode</span>
<span class="kn">from</span> <span class="nn">six.moves.urllib.request</span> <span class="kn">import</span> <span class="n">urlopen</span>
<span class="kn">from</span> <span class="nn">six.moves.urllib.error</span> <span class="kn">import</span> <span class="n">HTTPError</span>
</pre></div>
</div>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 and 3: alternative 4</span>
<span class="k">try</span><span class="p">:</span>
    <span class="kn">from</span> <span class="nn">urllib.parse</span> <span class="kn">import</span> <span class="n">urlparse</span><span class="p">,</span> <span class="n">urlencode</span>
    <span class="kn">from</span> <span class="nn">urllib.request</span> <span class="kn">import</span> <span class="n">urlopen</span><span class="p">,</span> <span class="n">Request</span>
    <span class="kn">from</span> <span class="nn">urllib.error</span> <span class="kn">import</span> <span class="n">HTTPError</span>
<span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span>
    <span class="kn">from</span> <span class="nn">urlparse</span> <span class="kn">import</span> <span class="n">urlparse</span>
    <span class="kn">from</span> <span class="nn">urllib</span> <span class="kn">import</span> <span class="n">urlencode</span>
    <span class="kn">from</span> <span class="nn">urllib2</span> <span class="kn">import</span> <span class="n">urlopen</span><span class="p">,</span> <span class="n">Request</span><span class="p">,</span> <span class="n">HTTPError</span>
</pre></div>
</div>
</div>
<div class="section" id="tkinter">
<h3>Tkinter<a class="headerlink" href="#tkinter" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">import</span> <span class="nn">Tkinter</span>
<span class="kn">import</span> <span class="nn">Dialog</span>
<span class="kn">import</span> <span class="nn">FileDialog</span>
<span class="kn">import</span> <span class="nn">ScrolledText</span>
<span class="kn">import</span> <span class="nn">SimpleDialog</span>
<span class="kn">import</span> <span class="nn">Tix</span>
<span class="kn">import</span> <span class="nn">Tkconstants</span>
<span class="kn">import</span> <span class="nn">Tkdnd</span>
<span class="kn">import</span> <span class="nn">tkColorChooser</span>
<span class="kn">import</span> <span class="nn">tkCommonDialog</span>
<span class="kn">import</span> <span class="nn">tkFileDialog</span>
<span class="kn">import</span> <span class="nn">tkFont</span>
<span class="kn">import</span> <span class="nn">tkMessageBox</span>
<span class="kn">import</span> <span class="nn">tkSimpleDialog</span>

<span class="c"># Python 2 and 3 (after ``pip install future``):</span>
<span class="kn">import</span> <span class="nn">tkinter</span>
<span class="kn">import</span> <span class="nn">tkinter.dialog</span>
<span class="kn">import</span> <span class="nn">tkinter.filedialog</span>
<span class="kn">import</span> <span class="nn">tkinter.scolledtext</span>
<span class="kn">import</span> <span class="nn">tkinter.simpledialog</span>
<span class="kn">import</span> <span class="nn">tkinter.tix</span>
<span class="kn">import</span> <span class="nn">tkinter.constants</span>
<span class="kn">import</span> <span class="nn">tkinter.dnd</span>
<span class="kn">import</span> <span class="nn">tkinter.colorchooser</span>
<span class="kn">import</span> <span class="nn">tkinter.commondialog</span>
<span class="kn">import</span> <span class="nn">tkinter.filedialog</span>
<span class="kn">import</span> <span class="nn">tkinter.font</span>
<span class="kn">import</span> <span class="nn">tkinter.messagebox</span>
<span class="kn">import</span> <span class="nn">tkinter.simpledialog</span>
</pre></div>
</div>
</div>
<div class="section" id="socketserver">
<h3>socketserver<a class="headerlink" href="#socketserver" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">import</span> <span class="nn">SocketServer</span>

<span class="c"># Python 2 and 3 (after ``pip install future``):</span>
<span class="kn">import</span> <span class="nn">socketserver</span>
</pre></div>
</div>
</div>
<div class="section" id="copy-reg-copyreg">
<h3>copy_reg, copyreg<a class="headerlink" href="#copy-reg-copyreg" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">import</span> <span class="nn">copy_reg</span>

<span class="c"># Python 2 and 3 (after ``pip install future``):</span>
<span class="kn">import</span> <span class="nn">copyreg</span>
</pre></div>
</div>
</div>
<div class="section" id="configparser">
<h3>configparser<a class="headerlink" href="#configparser" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">from</span> <span class="nn">ConfigParser</span> <span class="kn">import</span> <span class="n">ConfigParser</span>

<span class="c"># Python 2 and 3 (after ``pip install future``):</span>
<span class="kn">from</span> <span class="nn">configparser</span> <span class="kn">import</span> <span class="n">ConfigParser</span>
</pre></div>
</div>
</div>
<div class="section" id="queue">
<h3>queue<a class="headerlink" href="#queue" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">from</span> <span class="nn">Queue</span> <span class="kn">import</span> <span class="n">Queue</span><span class="p">,</span> <span class="n">heapq</span><span class="p">,</span> <span class="n">deque</span>

<span class="c"># Python 2 and 3 (after ``pip install future``):</span>
<span class="kn">from</span> <span class="nn">queue</span> <span class="kn">import</span> <span class="n">Queue</span><span class="p">,</span> <span class="n">heapq</span><span class="p">,</span> <span class="n">deque</span>
</pre></div>
</div>
</div>
<div class="section" id="repr-reprlib">
<h3>repr, reprlib<a class="headerlink" href="#repr-reprlib" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">from</span> <span class="nn">repr</span> <span class="kn">import</span> <span class="n">aRepr</span><span class="p">,</span> <span class="nb">repr</span>

<span class="c"># Python 2 and 3 (after ``pip install future``):</span>
<span class="kn">from</span> <span class="nn">reprlib</span> <span class="kn">import</span> <span class="n">aRepr</span><span class="p">,</span> <span class="nb">repr</span>
</pre></div>
</div>
</div>
<div class="section" id="userdict-userlist-userstring">
<h3>UserDict, UserList, UserString<a class="headerlink" href="#userdict-userlist-userstring" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">from</span> <span class="nn">UserDict</span> <span class="kn">import</span> <span class="n">UserDict</span>
<span class="kn">from</span> <span class="nn">UserList</span> <span class="kn">import</span> <span class="n">UserList</span>
<span class="kn">from</span> <span class="nn">UserString</span> <span class="kn">import</span> <span class="n">UserString</span>

<span class="c"># Python 3 only:</span>
<span class="kn">from</span> <span class="nn">collections</span> <span class="kn">import</span> <span class="n">UserDict</span><span class="p">,</span> <span class="n">UserList</span><span class="p">,</span> <span class="n">UserString</span>

<span class="c"># Python 2 and 3: alternative 1</span>
<span class="kn">from</span> <span class="nn">future.moves.collections</span> <span class="kn">import</span> <span class="n">UserDict</span><span class="p">,</span> <span class="n">UserList</span><span class="p">,</span> <span class="n">UserString</span>

<span class="c"># Python 2 and 3: alternative 2</span>
<span class="kn">from</span> <span class="nn">six.moves</span> <span class="kn">import</span> <span class="n">UserDict</span><span class="p">,</span> <span class="n">UserList</span><span class="p">,</span> <span class="n">UserString</span>

<span class="c"># Python 2 and 3: alternative 3</span>
<span class="kn">from</span> <span class="nn">future.standard_library</span> <span class="kn">import</span> <span class="n">install_aliases</span>
<span class="n">install_aliases</span><span class="p">()</span>
<span class="kn">from</span> <span class="nn">collections</span> <span class="kn">import</span> <span class="n">UserDict</span><span class="p">,</span> <span class="n">UserList</span><span class="p">,</span> <span class="n">UserString</span>
</pre></div>
</div>
</div>
<div class="section" id="itertools-filterfalse-zip-longest">
<h3>itertools: filterfalse, zip_longest<a class="headerlink" href="#itertools-filterfalse-zip-longest" title="Permalink to this headline">¶</a></h3>
<div class="code python highlight-python"><div class="highlight"><pre><span class="c"># Python 2 only:</span>
<span class="kn">from</span> <span class="nn">itertools</span> <span class="kn">import</span> <span class="n">ifilterfalse</span><span class="p">,</span> <span class="n">izip_longest</span>

<span class="c"># Python 3 only:</span>
<span class="kn">from</span> <span class="nn">itertools</span> <span class="kn">import</span> <span class="n">filterfalse</span><span class="p">,</span> <span class="n">zip_longest</span>

<span class="c"># Python 2 and 3: alternative 1</span>
<span class="kn">from</span> <span class="nn">future.moves.itertools</span> <span class="kn">import</span> <span class="n">filterfalse</span><span class="p">,</span> <span class="n">zip_longest</span>

<span class="c"># Python 2 and 3: alternative 2</span>
<span class="kn">from</span> <span class="nn">six.moves</span> <span class="kn">import</span> <span class="n">filterfalse</span><span class="p">,</span> <span class="n">zip_longest</span>

<span class="c"># Python 2 and 3: alternative 3</span>
<span class="kn">from</span> <span class="nn">future.standard_library</span> <span class="kn">import</span> <span class="n">install_aliases</span>
<span class="n">install_aliases</span><span class="p">()</span>
<span class="kn">from</span> <span class="nn">itertools</span> <span class="kn">import</span> <span class="n">filterfalse</span><span class="p">,</span> <span class="n">zip_longest</span>
</pre></div>
</div>
</div>
</div>
</div>


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