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<h2 class="title"><a name="re"></a>Chapter 7. Regular Expressions
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<li><span class="section"><a href="index.html#re.intro">7.1. Diving In</a></span></li>
<li><span class="section"><a href="street_addresses.html">7.2. Case Study: Street Addresses</a></span></li>
<li><span class="section"><a href="roman_numerals.html">7.3. Case Study: Roman Numerals</a></span><ul>
<li><span class="section"><a href="roman_numerals.html#d0e17592">7.3.1. Checking for Thousands</a></span></li>
<li><span class="section"><a href="roman_numerals.html#d0e17785">7.3.2. Checking for Hundreds</a></span></li>
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<li><span class="section"><a href="n_m_syntax.html">7.4. Using the {n,m} Syntax</a></span><ul>
<li><span class="section"><a href="n_m_syntax.html#d0e18326">7.4.1. Checking for Tens and Ones</a></span></li>
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<li><span class="section"><a href="verbose.html">7.5. Verbose Regular Expressions</a></span></li>
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<p>Regular expressions are a powerful and standardized way of searching, replacing, and parsing text with complex patterns of
characters. If you've used regular expressions in other languages (like <span class="application">Perl</span>), the syntax will be very familiar, and you get by just reading the summary of the <a href="http://www.python.org/doc/current/lib/module-re.html"><tt class="filename">re</tt> module</a> to get an overview of the available functions and their arguments.
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<h2 class="title"><a name="re.intro"></a>7.1. Diving In
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<p>Strings have methods for searching (<tt class="function">index</tt>, <tt class="function">find</tt>, and <tt class="function">count</tt>), replacing (<tt class="function">replace</tt>), and parsing (<tt class="function">split</tt>), but they are limited to the simplest of cases. The search methods look for a single, hard-coded substring, and they are
always case-sensitive. To do case-insensitive searches of a string <tt class="varname">s</tt>, you must call <tt class="function">s.lower()</tt> or <tt class="function">s.upper()</tt> and make sure your search strings are the appropriate case to match. The <tt class="function">replace</tt> and <tt class="function">split</tt> methods have the same limitations.
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<p>If what you're trying to do can be accomplished with string functions, you should use them. They're fast and simple and easy
to read, and there's a lot to be said for fast, simple, readable code. But if you find yourself using a lot of different
string functions with <tt class="literal">if</tt> statements to handle special cases, or if you're combining them with <tt class="function">split</tt> and <tt class="function">join</tt> and list comprehensions in weird unreadable ways, you may need to move up to regular expressions.
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<p>Although the regular expression syntax is tight and unlike normal code, the result can end up being <span class="emphasis"><em>more</em></span> readable than a hand-rolled solution that uses a long chain of string functions. There are even ways of embedding comments
within regular expressions to make them practically self-documenting.
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