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  <div class="section" id="module-tokenize">
<span id="tokenize-tokenizer-for-python-source"></span><h1>31.7. <a class="reference internal" href="#module-tokenize" title="tokenize: Lexical scanner for Python source code."><tt class="xref py py-mod docutils literal"><span class="pre">tokenize</span></tt></a> &#8212; Tokenizer for Python source<a class="headerlink" href="#module-tokenize" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="http://hg.python.org/cpython/file/2.7/Lib/tokenize.py">Lib/tokenize.py</a></p>
<hr class="docutils" />
<p>The <a class="reference internal" href="#module-tokenize" title="tokenize: Lexical scanner for Python source code."><tt class="xref py py-mod docutils literal"><span class="pre">tokenize</span></tt></a> module provides a lexical scanner for Python source code,
implemented in Python.  The scanner in this module returns comments as tokens as
well, making it useful for implementing &#8220;pretty-printers,&#8221; including colorizers
for on-screen displays.</p>
<p>To simplify token stream handling, all <a class="reference internal" href="../reference/lexical_analysis.html#operators"><em>Operators</em></a> and <a class="reference internal" href="../reference/lexical_analysis.html#delimiters"><em>Delimiters</em></a>
tokens are returned using the generic <a class="reference internal" href="token.html#token.OP" title="token.OP"><tt class="xref py py-data docutils literal"><span class="pre">token.OP</span></tt></a> token type.  The exact
type can be determined by checking the token <tt class="docutils literal"><span class="pre">string</span></tt> field on the
<a class="reference internal" href="../glossary.html#term-named-tuple"><em class="xref std std-term">named tuple</em></a> returned from <a class="reference internal" href="#tokenize.tokenize" title="tokenize.tokenize"><tt class="xref py py-func docutils literal"><span class="pre">tokenize.tokenize()</span></tt></a> for the character
sequence that identifies a specific operator token.</p>
<p>The primary entry point is a <a class="reference internal" href="../glossary.html#term-generator"><em class="xref std std-term">generator</em></a>:</p>
<dl class="function">
<dt id="tokenize.generate_tokens">
<tt class="descclassname">tokenize.</tt><tt class="descname">generate_tokens</tt><big>(</big><em>readline</em><big>)</big><a class="headerlink" href="#tokenize.generate_tokens" title="Permalink to this definition">¶</a></dt>
<dd><p>The <a class="reference internal" href="#tokenize.generate_tokens" title="tokenize.generate_tokens"><tt class="xref py py-func docutils literal"><span class="pre">generate_tokens()</span></tt></a> generator requires one argument, <em>readline</em>,
which must be a callable object which provides the same interface as the
<a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><tt class="xref py py-meth docutils literal"><span class="pre">readline()</span></tt></a> method of built-in file objects (see section
<a class="reference internal" href="stdtypes.html#bltin-file-objects"><em>File Objects</em></a>).  Each call to the function should return one line
of input as a string. Alternately, <em>readline</em> may be a callable object that
signals completion by raising <a class="reference internal" href="exceptions.html#exceptions.StopIteration" title="exceptions.StopIteration"><tt class="xref py py-exc docutils literal"><span class="pre">StopIteration</span></tt></a>.</p>
<p>The generator produces 5-tuples with these members: the token type; the token
string; a 2-tuple <tt class="docutils literal"><span class="pre">(srow,</span> <span class="pre">scol)</span></tt> of ints specifying the row and column
where the token begins in the source; a 2-tuple <tt class="docutils literal"><span class="pre">(erow,</span> <span class="pre">ecol)</span></tt> of ints
specifying the row and column where the token ends in the source; and the
line on which the token was found.  The line passed (the last tuple item) is
the <em>logical</em> line; continuation lines are included.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>

<p>An older entry point is retained for backward compatibility:</p>
<dl class="function">
<dt id="tokenize.tokenize">
<tt class="descclassname">tokenize.</tt><tt class="descname">tokenize</tt><big>(</big><em>readline</em><span class="optional">[</span>, <em>tokeneater</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#tokenize.tokenize" title="Permalink to this definition">¶</a></dt>
<dd><p>The <a class="reference internal" href="#module-tokenize" title="tokenize: Lexical scanner for Python source code."><tt class="xref py py-func docutils literal"><span class="pre">tokenize()</span></tt></a> function accepts two parameters: one representing the input
stream, and one providing an output mechanism for <a class="reference internal" href="#module-tokenize" title="tokenize: Lexical scanner for Python source code."><tt class="xref py py-func docutils literal"><span class="pre">tokenize()</span></tt></a>.</p>
<p>The first parameter, <em>readline</em>, must be a callable object which provides the
same interface as the <a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><tt class="xref py py-meth docutils literal"><span class="pre">readline()</span></tt></a> method of built-in file objects (see
section <a class="reference internal" href="stdtypes.html#bltin-file-objects"><em>File Objects</em></a>).  Each call to the function should return one
line of input as a string. Alternately, <em>readline</em> may be a callable object that
signals completion by raising <a class="reference internal" href="exceptions.html#exceptions.StopIteration" title="exceptions.StopIteration"><tt class="xref py py-exc docutils literal"><span class="pre">StopIteration</span></tt></a>.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.5: </span>Added <a class="reference internal" href="exceptions.html#exceptions.StopIteration" title="exceptions.StopIteration"><tt class="xref py py-exc docutils literal"><span class="pre">StopIteration</span></tt></a> support.</p>
<p>The second parameter, <em>tokeneater</em>, must also be a callable object.  It is
called once for each token, with five arguments, corresponding to the tuples
generated by <a class="reference internal" href="#tokenize.generate_tokens" title="tokenize.generate_tokens"><tt class="xref py py-func docutils literal"><span class="pre">generate_tokens()</span></tt></a>.</p>
</dd></dl>

<p>All constants from the <a class="reference internal" href="token.html#module-token" title="token: Constants representing terminal nodes of the parse tree."><tt class="xref py py-mod docutils literal"><span class="pre">token</span></tt></a> module are also exported from
<a class="reference internal" href="#module-tokenize" title="tokenize: Lexical scanner for Python source code."><tt class="xref py py-mod docutils literal"><span class="pre">tokenize</span></tt></a>, as are two additional token type values that might be passed to
the <em>tokeneater</em> function by <a class="reference internal" href="#module-tokenize" title="tokenize: Lexical scanner for Python source code."><tt class="xref py py-func docutils literal"><span class="pre">tokenize()</span></tt></a>:</p>
<dl class="data">
<dt id="tokenize.COMMENT">
<tt class="descclassname">tokenize.</tt><tt class="descname">COMMENT</tt><a class="headerlink" href="#tokenize.COMMENT" title="Permalink to this definition">¶</a></dt>
<dd><p>Token value used to indicate a comment.</p>
</dd></dl>

<dl class="data">
<dt id="tokenize.NL">
<tt class="descclassname">tokenize.</tt><tt class="descname">NL</tt><a class="headerlink" href="#tokenize.NL" title="Permalink to this definition">¶</a></dt>
<dd><p>Token value used to indicate a non-terminating newline.  The NEWLINE token
indicates the end of a logical line of Python code; NL tokens are generated when
a logical line of code is continued over multiple physical lines.</p>
</dd></dl>

<p>Another function is provided to reverse the tokenization process. This is useful
for creating tools that tokenize a script, modify the token stream, and write
back the modified script.</p>
<dl class="function">
<dt id="tokenize.untokenize">
<tt class="descclassname">tokenize.</tt><tt class="descname">untokenize</tt><big>(</big><em>iterable</em><big>)</big><a class="headerlink" href="#tokenize.untokenize" title="Permalink to this definition">¶</a></dt>
<dd><p>Converts tokens back into Python source code.  The <em>iterable</em> must return
sequences with at least two elements, the token type and the token string.  Any
additional sequence elements are ignored.</p>
<p>The reconstructed script is returned as a single string.  The result is
guaranteed to tokenize back to match the input so that the conversion is
lossless and round-trips are assured.  The guarantee applies only to the token
type and token string as the spacing between tokens (column positions) may
change.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5.</span></p>
</dd></dl>

<p>Example of a script re-writer that transforms float literals into Decimal
objects:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">decistmt</span><span class="p">(</span><span class="n">s</span><span class="p">):</span>
    <span class="sd">&quot;&quot;&quot;Substitute Decimals for floats in a string of statements.</span>

<span class="sd">    &gt;&gt;&gt; from decimal import Decimal</span>
<span class="sd">    &gt;&gt;&gt; s = &#39;print +21.3e-5*-.1234/81.7&#39;</span>
<span class="sd">    &gt;&gt;&gt; decistmt(s)</span>
<span class="sd">    &quot;print +Decimal (&#39;21.3e-5&#39;)*-Decimal (&#39;.1234&#39;)/Decimal (&#39;81.7&#39;)&quot;</span>

<span class="sd">    &gt;&gt;&gt; exec(s)</span>
<span class="sd">    -3.21716034272e-007</span>
<span class="sd">    &gt;&gt;&gt; exec(decistmt(s))</span>
<span class="sd">    -3.217160342717258261933904529E-7</span>

<span class="sd">    &quot;&quot;&quot;</span>
    <span class="n">result</span> <span class="o">=</span> <span class="p">[]</span>
    <span class="n">g</span> <span class="o">=</span> <span class="n">generate_tokens</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">s</span><span class="p">)</span><span class="o">.</span><span class="n">readline</span><span class="p">)</span>   <span class="c"># tokenize the string</span>
    <span class="k">for</span> <span class="n">toknum</span><span class="p">,</span> <span class="n">tokval</span><span class="p">,</span> <span class="n">_</span><span class="p">,</span> <span class="n">_</span><span class="p">,</span> <span class="n">_</span>  <span class="ow">in</span> <span class="n">g</span><span class="p">:</span>
        <span class="k">if</span> <span class="n">toknum</span> <span class="o">==</span> <span class="n">NUMBER</span> <span class="ow">and</span> <span class="s">&#39;.&#39;</span> <span class="ow">in</span> <span class="n">tokval</span><span class="p">:</span>  <span class="c"># replace NUMBER tokens</span>
            <span class="n">result</span><span class="o">.</span><span class="n">extend</span><span class="p">([</span>
                <span class="p">(</span><span class="n">NAME</span><span class="p">,</span> <span class="s">&#39;Decimal&#39;</span><span class="p">),</span>
                <span class="p">(</span><span class="n">OP</span><span class="p">,</span> <span class="s">&#39;(&#39;</span><span class="p">),</span>
                <span class="p">(</span><span class="n">STRING</span><span class="p">,</span> <span class="nb">repr</span><span class="p">(</span><span class="n">tokval</span><span class="p">)),</span>
                <span class="p">(</span><span class="n">OP</span><span class="p">,</span> <span class="s">&#39;)&#39;</span><span class="p">)</span>
            <span class="p">])</span>
        <span class="k">else</span><span class="p">:</span>
            <span class="n">result</span><span class="o">.</span><span class="n">append</span><span class="p">((</span><span class="n">toknum</span><span class="p">,</span> <span class="n">tokval</span><span class="p">))</span>
    <span class="k">return</span> <span class="n">untokenize</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
</pre></div>
</div>
</div>


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