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<h3>
Regular Expressions</h3>
<p>We already know that the <tT CLAss="monofont">string</tt> module is used to apply basic manipulation operations on strings; meanwhile, at the time of developing advanced routines, you might need to enhance Python's string-processing capabilities. That's when you should consider using the <A NAMe="idx1073745487"></a>
<a nAME="idx1073745488"></A>
<tt class="monofont">re</tt> module (<tt class="monofont">re</tt> stands for <i>regular expression</i>).</P>
<p>Regular expressions are strings, which contain a mix of text and special characters, that let you define complicated pattern matching and replacement rules for other strings.</p>
<P>Some of the special characters that compound regular expressions must be preceded by backslashes in order to be matched. Consequently, regular expressions are usually written as raw strings because they tend to use a lot of backslashes. That means that instead of writing <tt cLass="monofont">"\\b(usa)\\d",</tT> it is much easier to say <tt cLASS="monofont">r"\b(usa)\d".</tt>
</p>
<p>Older versions of Python used to support the following regular expression obsolete modules are: <TT CLass="monofont">regexp, regex,</tT> and <TT Class="monofont">regsub.</TT>
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