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<li class="toctree-l1 current"><a class="current reference internal" href="">Quick-start guide</a><ul>
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<li class="toctree-l2"><a class="reference internal" href="#to-convert-existing-python-2-code">To convert existing Python 2 code</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>
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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>
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<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>
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<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>
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<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>
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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>
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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>
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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>
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  <h4>Easy, clean, reliable Python 2/3 compatibility</h4>
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<li class="toctree-l1"><a class="reference internal" href="whatsnew.html">What&#8217;s New</a></li>
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<li class="toctree-l1 current"><a class="current reference internal" href="">Quick-start guide</a><ul>
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  <div class="section" id="quick-start-guide">
<span id="quickstart-guide"></span><h1>Quick-start guide<a class="headerlink" href="#quick-start-guide" title="Permalink to this headline">¶</a></h1>
<p>You can use <code class="docutils literal"><span class="pre">future</span></code> to help to port your code from Python 2 to Python 3
today &#8211; and still have it run on Python 2.</p>
<p>If you already have Python 3 code, you can instead use <code class="docutils literal"><span class="pre">future</span></code> to
offer Python 2 compatibility with almost no extra work.</p>
<div class="section" id="installation">
<h2>Installation<a class="headerlink" href="#installation" title="Permalink to this headline">¶</a></h2>
<p>To install the latest stable version, type:</p>
<div class="highlight-python"><div class="highlight"><pre>pip install future
</pre></div>
</div>
<p>If you would prefer the latest development version, it is available <a class="reference external" href="https://github.com/PythonCharmers/python-future">here</a>.</p>
<p>On Python 2.6, three packages containing backports of standard library modules
in Python 2.7+ are needed for small parts of the code:</p>
<div class="highlight-python"><div class="highlight"><pre>pip install importlib       # for future.standard_library.import_ function only
pip install unittest2       # to run the test suite
pip install argparse        # for the backported http.server module from Py3.3
</pre></div>
</div>
<p>Unless these features are used on Python 2.6 (only), <code class="docutils literal"><span class="pre">future</span></code> has no
dependencies.</p>
</div>
<div class="section" id="if-you-are-writing-code-from-scratch">
<h2>If you are writing code from scratch<a class="headerlink" href="#if-you-are-writing-code-from-scratch" title="Permalink to this headline">¶</a></h2>
<p>The easiest way is to start each new module with these lines:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="p">(</span><span class="n">absolute_import</span><span class="p">,</span> <span class="n">division</span><span class="p">,</span>
                        <span class="n">print_function</span><span class="p">,</span> <span class="n">unicode_literals</span><span class="p">)</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="o">*</span>
</pre></div>
</div>
<p>Then write standard Python 3 code. The <code class="xref py py-mod docutils literal"><span class="pre">future</span></code> package will
provide support for running your code on Python 2.6, 2.7, and 3.3+ mostly
unchanged.</p>
<ul class="simple">
<li>For explicit import forms, see <a class="reference internal" href="imports.html#explicit-imports"><span>Explicit imports</span></a>.</li>
<li>For more details, see <a class="reference internal" href="what_else.html#what-else"><span>What else you need to know</span></a>.</li>
<li>For a cheat sheet, see <a class="reference internal" href="compatible_idioms.html#compatible-idioms"><span>Cheat Sheet: Writing Python 2-3 compatible code</span></a>.</li>
</ul>
</div>
<div class="section" id="to-convert-existing-python-3-code">
<h2>To convert existing Python 3 code<a class="headerlink" href="#to-convert-existing-python-3-code" title="Permalink to this headline">¶</a></h2>
<p>To offer backward compatibility with Python 2 from your Python 3 code,
you can use the <code class="docutils literal"><span class="pre">pasteurize</span></code> script. This adds these lines at the top of each
module:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">absolute_import</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">division</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">unicode_literals</span>

<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">open</span>
<span class="kn">from</span> <span class="nn">builtins</span> <span class="kn">import</span> <span class="nb">str</span>
<span class="c"># etc., as needed</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>
</pre></div>
</div>
<p>and converts several Python 3-only constructs (like keyword-only arguments) to a
form compatible with both Py3 and Py2. Most remaining Python 3 code should
simply work on Python 2.</p>
<p>See <a class="reference internal" href="pasteurize.html#backwards-conversion"><span>pasteurize: Py3 to Py2/3</span></a> for more details.</p>
</div>
<div class="section" id="to-convert-existing-python-2-code">
<h2>To convert existing Python 2 code<a class="headerlink" href="#to-convert-existing-python-2-code" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal"><span class="pre">futurize</span></code> script passes Python 2 code through all the appropriate fixers
to turn it into valid Python 3 code, and then adds <code class="docutils literal"><span class="pre">__future__</span></code> and
<code class="docutils literal"><span class="pre">future</span></code> package imports to re-enable compatibility with Python 2.</p>
<p>For example, running <code class="docutils literal"><span class="pre">futurize</span></code> turns this Python 2 code:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">ConfigParser</span>                 <span class="c"># Py2 module name</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 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="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">print</span> <span class="nb">next</span><span class="p">(</span><span class="n">itr</span><span class="p">),</span>
<span class="k">for</span> <span class="n">letter</span> <span class="ow">in</span> <span class="n">itr</span><span class="p">:</span>
    <span class="k">print</span> <span class="n">letter</span><span class="p">,</span>                   <span class="c"># Py2-style print statement</span>
</pre></div>
</div>
<p>into this code which runs on both Py2 and Py3:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</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">future.builtins</span> <span class="kn">import</span> <span class="nb">next</span>
<span class="kn">from</span> <span class="nn">future.builtins</span> <span class="kn">import</span> <span class="nb">object</span>
<span class="kn">import</span> <span class="nn">configparser</span>                 <span class="c"># Py3-style import</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="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">print</span><span class="p">(</span><span class="nb">next</span><span class="p">(</span><span class="n">itr</span><span class="p">),</span> <span class="n">end</span><span class="o">=</span><span class="s">&#39; &#39;</span><span class="p">)</span>           <span class="c"># Py3-style print function</span>
<span class="k">for</span> <span class="n">letter</span> <span class="ow">in</span> <span class="n">itr</span><span class="p">:</span>
    <span class="k">print</span><span class="p">(</span><span class="n">letter</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>
<p>To write out all the changes to your Python files that <code class="docutils literal"><span class="pre">futurize</span></code> suggests,
use the <code class="docutils literal"><span class="pre">-w</span></code> flag.</p>
<p>For complex projects, it is probably best to divide the porting into two stages.
Stage 1 is for &#8220;safe&#8221; changes that modernize the code but do not break Python
2.6 compatibility or introduce a depdendency on the <code class="docutils literal"><span class="pre">future</span></code> package. Stage 2
is to complete the process.</p>
<p>See <a class="reference internal" href="futurize.html#forwards-conversion-stage1"><span>Stage 1: &#8220;safe&#8221; fixes</span></a> and <a class="reference internal" href="futurize.html#forwards-conversion-stage2"><span>Stage 2: Py3-style code with wrappers for Py2</span></a> for more details.</p>
</div>
<div class="section" id="standard-library-reorganization">
<span id="standard-library"></span><h2>Standard library reorganization<a class="headerlink" href="#standard-library-reorganization" title="Permalink to this headline">¶</a></h2>
<p><code class="xref py py-mod docutils literal"><span class="pre">future</span></code> supports the standard library reorganization (PEP 3108) via
one of several mechanisms, allowing most moved standard library modules
to be accessed under their Python 3 names and locations in Python 2:</p>
<div class="highlight-python"><div class="highlight"><pre><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="c"># Then these Py3-style imports work on both Python 2 and Python 3:</span>
<span class="kn">import</span> <span class="nn">socketserver</span>
<span class="kn">import</span> <span class="nn">queue</span>
<span class="kn">import</span> <span class="nn">configparser</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="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="p">,</span> <span class="n">ChainMap</span>   <span class="c"># even on Py2.6</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="kn">import</span> <span class="nn">html</span>
<span class="kn">import</span> <span class="nn">html.entities</span>
<span class="kn">import</span> <span class="nn">html.parser</span>

<span class="kn">import</span> <span class="nn">http</span>
<span class="kn">import</span> <span class="nn">http.client</span>
<span class="kn">import</span> <span class="nn">http.server</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">urllib.request</span>
<span class="kn">import</span> <span class="nn">urllib.parse</span>
<span class="kn">import</span> <span class="nn">urllib.response</span>
<span class="kn">import</span> <span class="nn">urllib.error</span>
<span class="kn">import</span> <span class="nn">urllib.robotparser</span>

<span class="kn">import</span> <span class="nn">xmlrpc.client</span>
<span class="kn">import</span> <span class="nn">xmlrpc.server</span>
</pre></div>
</div>
<p>and others. For a complete list, see <a class="reference internal" href="standard_library_imports.html#direct-imports"><span>Direct imports</span></a>.</p>
</div>
<div class="section" id="python-2-only-dependencies">
<span id="py2-dependencies"></span><h2>Python 2-only dependencies<a class="headerlink" href="#python-2-only-dependencies" title="Permalink to this headline">¶</a></h2>
<p>If you have dependencies that support only Python 2, you may be able to use the
<code class="docutils literal"><span class="pre">past</span></code> module to automatically translate these Python 2 modules to Python 3
upon import. First, install the Python 2-only package into your Python 3
environment:</p>
<div class="highlight-python"><div class="highlight"><pre>$ pip3 install mypackagename --no-compile   # to ignore SyntaxErrors
</pre></div>
</div>
<p>(or use <code class="docutils literal"><span class="pre">pip</span></code> if this points to your Py3 environment.)</p>
<p>Then add the following code at the top of your (Py3 or Py2/3-compatible)
code:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">past</span> <span class="kn">import</span> <span class="n">autotranslate</span>
<span class="n">autotranslate</span><span class="p">([</span><span class="s">&#39;mypackagename&#39;</span><span class="p">])</span>
<span class="kn">import</span> <span class="nn">mypackagename</span>
</pre></div>
</div>
<p>This feature is experimental, and we would appreciate your feedback on
how well this works or doesn&#8217;t work for you. Please file an issue <a class="reference external" href="https://github.com/PythonCharmers/python-future">here</a> or post to the
<a class="reference external" href="https://mail.python.org/mailman/listinfo/python-porting">python-porting</a>
mailing list.</p>
<p>For more information on the automatic translation feature, see <a class="reference internal" href="translation.html#translation"><span>Using Python 2-only dependencies on Python 3</span></a>.</p>
</div>
<div class="section" id="next-steps">
<h2>Next steps<a class="headerlink" href="#next-steps" title="Permalink to this headline">¶</a></h2>
<p>For more information about writing Py2/3-compatible code, see:</p>
<ul class="simple">
<li><a class="reference internal" href="compatible_idioms.html#compatible-idioms"><span>Cheat Sheet: Writing Python 2-3 compatible code</span></a></li>
<li><a class="reference internal" href="what_else.html#what-else"><span>What else you need to know</span></a>.</li>
</ul>
</div>
</div>


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