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<div class="section" id="to3-automated-python-2-to-3-code-translation">
<span id="to3-reference"></span><h1>25.4. 2to3 - Automated Python 2 to 3 code translation<a class="headerlink" href="#to3-automated-python-2-to-3-code-translation" title="Permalink to this headline">¶</a></h1>
<p>2to3 is a Python program that reads Python 2.x source code and applies a series
of <em>fixers</em> to transform it into valid Python 3.x code. The standard library
contains a rich set of fixers that will handle almost all code. 2to3 supporting
library <tt class="xref docutils literal"><span class="pre">lib2to3</span></tt> is, however, a flexible and generic library, so it is
possible to write your own fixers for 2to3. <tt class="xref docutils literal"><span class="pre">lib2to3</span></tt> could also be
adapted to custom applications in which Python code needs to be edited
automatically.</p>
<div class="section" id="using-2to3">
<span id="to3-using"></span><h2>25.4.1. Using 2to3<a class="headerlink" href="#using-2to3" title="Permalink to this headline">¶</a></h2>
<p>2to3 will usually be installed with the Python interpreter as a script. It is
also located in the <tt class="docutils literal"><span class="pre">Tools/scripts</span></tt> directory of the Python root.</p>
<p>2to3’s basic arguments are a list of files or directories to transform. The
directories are to recursively traversed for Python sources.</p>
<p>Here is a sample Python 2.x source file, <tt class="docutils literal"><span class="pre">example.py</span></tt>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">greet</span><span class="p">(</span><span class="n">name</span><span class="p">):</span>
<span class="k">print</span> <span class="s">"Hello, {0}!"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">name</span><span class="p">)</span>
<span class="k">print</span> <span class="s">"What's your name?"</span>
<span class="n">name</span> <span class="o">=</span> <span class="nb">raw_input</span><span class="p">()</span>
<span class="n">greet</span><span class="p">(</span><span class="n">name</span><span class="p">)</span>
</pre></div>
</div>
<p>It can be converted to Python 3.x code via 2to3 on the command line:</p>
<div class="highlight-python"><pre>$ 2to3 example.py</pre>
</div>
<p>A diff against the original source file is printed. 2to3 can also write the
needed modifications right back to the source file. (A backup of the original
file is made unless <em class="xref">-n</em> is also given.) Writing the changes back is
enabled with the <em class="xref">-w</em> flag:</p>
<div class="highlight-python"><pre>$ 2to3 -w example.py</pre>
</div>
<p>After transformation, <tt class="docutils literal"><span class="pre">example.py</span></tt> looks like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">greet</span><span class="p">(</span><span class="n">name</span><span class="p">):</span>
<span class="k">print</span><span class="p">(</span><span class="s">"Hello, {0}!"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">name</span><span class="p">))</span>
<span class="k">print</span><span class="p">(</span><span class="s">"What's your name?"</span><span class="p">)</span>
<span class="n">name</span> <span class="o">=</span> <span class="nb">input</span><span class="p">()</span>
<span class="n">greet</span><span class="p">(</span><span class="n">name</span><span class="p">)</span>
</pre></div>
</div>
<p>Comments and exact indentation are preserved throughout the translation process.</p>
<p>By default, 2to3 runs a set of <a class="reference internal" href="#to3-fixers"><em>predefined fixers</em></a>. The
<em class="xref">-l</em> flag lists all available fixers. An explicit set of fixers to run
can be given with <em class="xref">-f</em>. Likewise the <a class="reference external" href="../using/cmdline.html#cmdoption-x"><em class="xref">-x</em></a> explicitly disables a
fixer. The following example runs only the <tt class="docutils literal"><span class="pre">imports</span></tt> and <tt class="docutils literal"><span class="pre">has_key</span></tt> fixers:</p>
<div class="highlight-python"><pre>$ 2to3 -f imports -f has_key example.py</pre>
</div>
<p>This command runs every fixer except the <tt class="docutils literal"><span class="pre">apply</span></tt> fixer:</p>
<div class="highlight-python"><pre>$ 2to3 -x apply example.py</pre>
</div>
<p>Some fixers are <em>explicit</em>, meaning they aren’t run by default and must be
listed on the command line to be run. Here, in addition to the default fixers,
the <tt class="docutils literal"><span class="pre">idioms</span></tt> fixer is run:</p>
<div class="highlight-python"><pre>$ 2to3 -f all -f idioms example.py</pre>
</div>
<p>Notice how passing <tt class="docutils literal"><span class="pre">all</span></tt> enables all default fixers.</p>
<p>Sometimes 2to3 will find a place in your source code that needs to be changed,
but 2to3 cannot fix automatically. In this case, 2to3 will print a warning
beneath the diff for a file. You should address the warning in order to have
compliant 3.x code.</p>
<p>2to3 can also refactor doctests. To enable this mode, use the <a class="reference external" href="../using/cmdline.html#cmdoption-d"><em class="xref">-d</em></a>
flag. Note that <em>only</em> doctests will be refactored. This also doesn’t require
the module to be valid Python. For example, doctest like examples in a reST
document could also be refactored with this option.</p>
<p>The <a class="reference external" href="../using/cmdline.html#cmdoption-v"><em class="xref">-v</em></a> option enables output of more information on the translation
process.</p>
<p>Since some print statements can be parsed as function calls or statements, 2to3
cannot always read files containing the print function. When 2to3 detects the
presence of the <tt class="docutils literal"><span class="pre">from</span> <span class="pre">__future__</span> <span class="pre">import</span> <span class="pre">print_function</span></tt> compiler directive, it
modifies its internal grammar to interpert <a title="print" class="reference external" href="functions.html#print"><tt class="xref docutils literal"><span class="pre">print()</span></tt></a> as a function. This
change can also be enabled manually with the <em class="xref">-p</em> flag. Use
<em class="xref">-p</em> to run fixers on code that already has had its print statements
converted.</p>
</div>
<div class="section" id="fixers">
<span id="to3-fixers"></span><h2>25.4.2. Fixers<a class="headerlink" href="#fixers" title="Permalink to this headline">¶</a></h2>
<p>Each step of transforming code is encapsulated in a fixer. The command <tt class="docutils literal"><span class="pre">2to3</span>
<span class="pre">-l</span></tt> lists them. As <a class="reference internal" href="#to3-using"><em>documented above</em></a>, each can be turned on
and off individually. They are described here in more detail.</p>
<dl class="2to3fixer">
<dt id="2to3fixer-apply">
<tt class="descname">apply</tt><a class="headerlink" href="#2to3fixer-apply" title="Permalink to this definition">¶</a></dt>
<dd>Removes usage of <a title="apply" class="reference external" href="functions.html#apply"><tt class="xref docutils literal"><span class="pre">apply()</span></tt></a>. For example <tt class="docutils literal"><span class="pre">apply(function,</span> <span class="pre">*args,</span>
<span class="pre">**kwargs)</span></tt> is converted to <tt class="docutils literal"><span class="pre">function(*args,</span> <span class="pre">**kwargs)</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-basestring">
<tt class="descname">basestring</tt><a class="headerlink" href="#2to3fixer-basestring" title="Permalink to this definition">¶</a></dt>
<dd>Converts <a title="basestring" class="reference external" href="functions.html#basestring"><tt class="xref docutils literal"><span class="pre">basestring</span></tt></a> to <a title="str" class="reference external" href="functions.html#str"><tt class="xref docutils literal"><span class="pre">str</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-buffer">
<tt class="descname">buffer</tt><a class="headerlink" href="#2to3fixer-buffer" title="Permalink to this definition">¶</a></dt>
<dd>Converts <a title="buffer" class="reference external" href="functions.html#buffer"><tt class="xref docutils literal"><span class="pre">buffer</span></tt></a> to <tt class="xref docutils literal"><span class="pre">memoryview</span></tt>. This fixer is optional
because the <tt class="xref docutils literal"><span class="pre">memoryview</span></tt> API is similar but not exactly the same as
that of <a title="buffer" class="reference external" href="functions.html#buffer"><tt class="xref docutils literal"><span class="pre">buffer</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-callable">
<tt class="descname">callable</tt><a class="headerlink" href="#2to3fixer-callable" title="Permalink to this definition">¶</a></dt>
<dd>Converts <tt class="docutils literal"><span class="pre">callable(x)</span></tt> to <tt class="docutils literal"><span class="pre">isinstance(x,</span> <span class="pre">collections.Callable)</span></tt>, adding
an import to <a title="High-performance datatypes" class="reference external" href="collections.html#module-collections"><tt class="xref docutils literal"><span class="pre">collections</span></tt></a> if needed.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-dict">
<tt class="descname">dict</tt><a class="headerlink" href="#2to3fixer-dict" title="Permalink to this definition">¶</a></dt>
<dd>Fixes dictionary iteration methods. <a title="dict.iteritems" class="reference external" href="stdtypes.html#dict.iteritems"><tt class="xref docutils literal"><span class="pre">dict.iteritems()</span></tt></a> is converted to
<a title="dict.items" class="reference external" href="stdtypes.html#dict.items"><tt class="xref docutils literal"><span class="pre">dict.items()</span></tt></a>, <a title="dict.iterkeys" class="reference external" href="stdtypes.html#dict.iterkeys"><tt class="xref docutils literal"><span class="pre">dict.iterkeys()</span></tt></a> to <a title="dict.keys" class="reference external" href="stdtypes.html#dict.keys"><tt class="xref docutils literal"><span class="pre">dict.keys()</span></tt></a>, and
<a title="dict.itervalues" class="reference external" href="stdtypes.html#dict.itervalues"><tt class="xref docutils literal"><span class="pre">dict.itervalues()</span></tt></a> to <a title="dict.values" class="reference external" href="stdtypes.html#dict.values"><tt class="xref docutils literal"><span class="pre">dict.values()</span></tt></a>. Similarly,
<tt class="xref docutils literal"><span class="pre">dict.viewitems()</span></tt>, <tt class="xref docutils literal"><span class="pre">dict.viewkeys()</span></tt> and <tt class="xref docutils literal"><span class="pre">dict.viewvalues()</span></tt> are
converted respectively to <a title="dict.items" class="reference external" href="stdtypes.html#dict.items"><tt class="xref docutils literal"><span class="pre">dict.items()</span></tt></a>, <a title="dict.keys" class="reference external" href="stdtypes.html#dict.keys"><tt class="xref docutils literal"><span class="pre">dict.keys()</span></tt></a> and
<a title="dict.values" class="reference external" href="stdtypes.html#dict.values"><tt class="xref docutils literal"><span class="pre">dict.values()</span></tt></a>. It also wraps existing usages of <a title="dict.items" class="reference external" href="stdtypes.html#dict.items"><tt class="xref docutils literal"><span class="pre">dict.items()</span></tt></a>,
<a title="dict.keys" class="reference external" href="stdtypes.html#dict.keys"><tt class="xref docutils literal"><span class="pre">dict.keys()</span></tt></a>, and <a title="dict.values" class="reference external" href="stdtypes.html#dict.values"><tt class="xref docutils literal"><span class="pre">dict.values()</span></tt></a> in a call to <a title="list" class="reference external" href="functions.html#list"><tt class="xref docutils literal"><span class="pre">list</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-except">
<tt class="descname">except</tt><a class="headerlink" href="#2to3fixer-except" title="Permalink to this definition">¶</a></dt>
<dd>Converts <tt class="docutils literal"><span class="pre">except</span> <span class="pre">X,</span> <span class="pre">T</span></tt> to <tt class="docutils literal"><span class="pre">except</span> <span class="pre">X</span> <span class="pre">as</span> <span class="pre">T</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-exec">
<tt class="descname">exec</tt><a class="headerlink" href="#2to3fixer-exec" title="Permalink to this definition">¶</a></dt>
<dd>Converts the <a class="reference external" href="../reference/simple_stmts.html#exec"><tt class="xref docutils literal"><span class="pre">exec</span></tt></a> statement to the <tt class="xref docutils literal"><span class="pre">exec()</span></tt> function.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-execfile">
<tt class="descname">execfile</tt><a class="headerlink" href="#2to3fixer-execfile" title="Permalink to this definition">¶</a></dt>
<dd>Removes usage of <a title="execfile" class="reference external" href="functions.html#execfile"><tt class="xref docutils literal"><span class="pre">execfile()</span></tt></a>. The argument to <a title="execfile" class="reference external" href="functions.html#execfile"><tt class="xref docutils literal"><span class="pre">execfile()</span></tt></a> is
wrapped in calls to <a title="open" class="reference external" href="functions.html#open"><tt class="xref docutils literal"><span class="pre">open()</span></tt></a>, <a title="compile" class="reference external" href="functions.html#compile"><tt class="xref docutils literal"><span class="pre">compile()</span></tt></a>, and <tt class="xref docutils literal"><span class="pre">exec()</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-exitfunc">
<tt class="descname">exitfunc</tt><a class="headerlink" href="#2to3fixer-exitfunc" title="Permalink to this definition">¶</a></dt>
<dd>Changes assignment of <a title="sys.exitfunc" class="reference external" href="sys.html#sys.exitfunc"><tt class="xref docutils literal"><span class="pre">sys.exitfunc</span></tt></a> to use of the <a title="Register and execute cleanup functions." class="reference external" href="atexit.html#module-atexit"><tt class="xref docutils literal"><span class="pre">atexit</span></tt></a>
module.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-filter">
<tt class="descname">filter</tt><a class="headerlink" href="#2to3fixer-filter" title="Permalink to this definition">¶</a></dt>
<dd>Wraps <a title="filter" class="reference external" href="functions.html#filter"><tt class="xref docutils literal"><span class="pre">filter()</span></tt></a> usage in a <a title="list" class="reference external" href="functions.html#list"><tt class="xref docutils literal"><span class="pre">list</span></tt></a> call.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-funcattrs">
<tt class="descname">funcattrs</tt><a class="headerlink" href="#2to3fixer-funcattrs" title="Permalink to this definition">¶</a></dt>
<dd>Fixes function attributes that have been renamed. For example,
<tt class="docutils literal"><span class="pre">my_function.func_closure</span></tt> is converted to <tt class="docutils literal"><span class="pre">my_function.__closure__</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-future">
<tt class="descname">future</tt><a class="headerlink" href="#2to3fixer-future" title="Permalink to this definition">¶</a></dt>
<dd>Removes <tt class="docutils literal"><span class="pre">from</span> <span class="pre">__future__</span> <span class="pre">import</span> <span class="pre">new_feature</span></tt> statements.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-getcwdu">
<tt class="descname">getcwdu</tt><a class="headerlink" href="#2to3fixer-getcwdu" title="Permalink to this definition">¶</a></dt>
<dd>Renames <a title="os.getcwdu" class="reference external" href="os.html#os.getcwdu"><tt class="xref docutils literal"><span class="pre">os.getcwdu()</span></tt></a> to <a title="os.getcwd" class="reference external" href="os.html#os.getcwd"><tt class="xref docutils literal"><span class="pre">os.getcwd()</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-has_key">
<tt class="descname">has_key</tt><a class="headerlink" href="#2to3fixer-has_key" title="Permalink to this definition">¶</a></dt>
<dd>Changes <tt class="docutils literal"><span class="pre">dict.has_key(key)</span></tt> to <tt class="docutils literal"><span class="pre">key</span> <span class="pre">in</span> <span class="pre">dict</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-idioms">
<tt class="descname">idioms</tt><a class="headerlink" href="#2to3fixer-idioms" title="Permalink to this definition">¶</a></dt>
<dd><p>This optional fixer performs several transformations that make Python code
more idiomatic. Type comparisons like <tt class="docutils literal"><span class="pre">type(x)</span> <span class="pre">is</span> <span class="pre">SomeClass</span></tt> and
<tt class="docutils literal"><span class="pre">type(x)</span> <span class="pre">==</span> <span class="pre">SomeClass</span></tt> are converted to <tt class="docutils literal"><span class="pre">isinstance(x,</span> <span class="pre">SomeClass)</span></tt>.
<tt class="docutils literal"><span class="pre">while</span> <span class="pre">1</span></tt> becomes <tt class="docutils literal"><span class="pre">while</span> <span class="pre">True</span></tt>. This fixer also tries to make use of
<a title="sorted" class="reference external" href="functions.html#sorted"><tt class="xref docutils literal"><span class="pre">sorted()</span></tt></a> in appropriate places. For example, this block</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">L</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">some_iterable</span><span class="p">)</span>
<span class="n">L</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span>
</pre></div>
</div>
<p>is changed to</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">L</span> <span class="o">=</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">some_iterable</span><span class="p">)</span>
</pre></div>
</div>
</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-import">
<tt class="descname">import</tt><a class="headerlink" href="#2to3fixer-import" title="Permalink to this definition">¶</a></dt>
<dd>Detects sibling imports and converts them to relative imports.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-imports">
<tt class="descname">imports</tt><a class="headerlink" href="#2to3fixer-imports" title="Permalink to this definition">¶</a></dt>
<dd>Handles module renames in the standard library.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-imports2">
<tt class="descname">imports2</tt><a class="headerlink" href="#2to3fixer-imports2" title="Permalink to this definition">¶</a></dt>
<dd>Handles other modules renames in the standard library. It is separate from
the <a class="reference internal" href="#2to3fixer-imports"><tt class="xref docutils literal"><span class="pre">imports</span></tt></a> fixer only because of technical limitations.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-input">
<tt class="descname">input</tt><a class="headerlink" href="#2to3fixer-input" title="Permalink to this definition">¶</a></dt>
<dd>Converts <tt class="docutils literal"><span class="pre">input(prompt)</span></tt> to <tt class="docutils literal"><span class="pre">eval(input(prompt))</span></tt></dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-intern">
<tt class="descname">intern</tt><a class="headerlink" href="#2to3fixer-intern" title="Permalink to this definition">¶</a></dt>
<dd>Converts <a title="intern" class="reference external" href="functions.html#intern"><tt class="xref docutils literal"><span class="pre">intern()</span></tt></a> to <tt class="xref docutils literal"><span class="pre">sys.intern()</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-isinstance">
<tt class="descname">isinstance</tt><a class="headerlink" href="#2to3fixer-isinstance" title="Permalink to this definition">¶</a></dt>
<dd>Fixes duplicate types in the second argument of <a title="isinstance" class="reference external" href="functions.html#isinstance"><tt class="xref docutils literal"><span class="pre">isinstance()</span></tt></a>. For
example, <tt class="docutils literal"><span class="pre">isinstance(x,</span> <span class="pre">(int,</span> <span class="pre">int))</span></tt> is converted to <tt class="docutils literal"><span class="pre">isinstance(x,</span>
<span class="pre">(int))</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-itertools_imports">
<tt class="descname">itertools_imports</tt><a class="headerlink" href="#2to3fixer-itertools_imports" title="Permalink to this definition">¶</a></dt>
<dd>Removes imports of <a title="itertools.ifilter" class="reference external" href="itertools.html#itertools.ifilter"><tt class="xref docutils literal"><span class="pre">itertools.ifilter()</span></tt></a>, <a title="itertools.izip" class="reference external" href="itertools.html#itertools.izip"><tt class="xref docutils literal"><span class="pre">itertools.izip()</span></tt></a>, and
<a title="itertools.imap" class="reference external" href="itertools.html#itertools.imap"><tt class="xref docutils literal"><span class="pre">itertools.imap()</span></tt></a>. Imports of <a title="itertools.ifilterfalse" class="reference external" href="itertools.html#itertools.ifilterfalse"><tt class="xref docutils literal"><span class="pre">itertools.ifilterfalse()</span></tt></a> are also
changed to <tt class="xref docutils literal"><span class="pre">itertools.filterfalse()</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-itertools">
<tt class="descname">itertools</tt><a class="headerlink" href="#2to3fixer-itertools" title="Permalink to this definition">¶</a></dt>
<dd>Changes usage of <a title="itertools.ifilter" class="reference external" href="itertools.html#itertools.ifilter"><tt class="xref docutils literal"><span class="pre">itertools.ifilter()</span></tt></a>, <a title="itertools.izip" class="reference external" href="itertools.html#itertools.izip"><tt class="xref docutils literal"><span class="pre">itertools.izip()</span></tt></a>, and
<a title="itertools.imap" class="reference external" href="itertools.html#itertools.imap"><tt class="xref docutils literal"><span class="pre">itertools.imap()</span></tt></a> to their built-in equivalents.
<a title="itertools.ifilterfalse" class="reference external" href="itertools.html#itertools.ifilterfalse"><tt class="xref docutils literal"><span class="pre">itertools.ifilterfalse()</span></tt></a> is changed to <tt class="xref docutils literal"><span class="pre">itertools.filterfalse()</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-long">
<tt class="descname">long</tt><a class="headerlink" href="#2to3fixer-long" title="Permalink to this definition">¶</a></dt>
<dd>Strips the <tt class="docutils literal"><span class="pre">L</span></tt> prefix on long literals and renames <a title="long" class="reference external" href="functions.html#long"><tt class="xref docutils literal"><span class="pre">long</span></tt></a> to
<a title="int" class="reference external" href="functions.html#int"><tt class="xref docutils literal"><span class="pre">int</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-map">
<tt class="descname">map</tt><a class="headerlink" href="#2to3fixer-map" title="Permalink to this definition">¶</a></dt>
<dd>Wraps <a title="map" class="reference external" href="functions.html#map"><tt class="xref docutils literal"><span class="pre">map()</span></tt></a> in a <a title="list" class="reference external" href="functions.html#list"><tt class="xref docutils literal"><span class="pre">list</span></tt></a> call. It also changes <tt class="docutils literal"><span class="pre">map(None,</span> <span class="pre">x)</span></tt>
to <tt class="docutils literal"><span class="pre">list(x)</span></tt>. Using <tt class="docutils literal"><span class="pre">from</span> <span class="pre">future_builtins</span> <span class="pre">import</span> <span class="pre">map</span></tt> disables this
fixer.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-metaclass">
<tt class="descname">metaclass</tt><a class="headerlink" href="#2to3fixer-metaclass" title="Permalink to this definition">¶</a></dt>
<dd>Converts the old metaclass syntax (<tt class="docutils literal"><span class="pre">__metaclass__</span> <span class="pre">=</span> <span class="pre">Meta</span></tt> in the class
body) to the new (<tt class="docutils literal"><span class="pre">class</span> <span class="pre">X(metaclass=Meta)</span></tt>).</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-methodattrs">
<tt class="descname">methodattrs</tt><a class="headerlink" href="#2to3fixer-methodattrs" title="Permalink to this definition">¶</a></dt>
<dd>Fixes old method attribute names. For example, <tt class="docutils literal"><span class="pre">meth.im_func</span></tt> is converted
to <tt class="docutils literal"><span class="pre">meth.__func__</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-ne">
<tt class="descname">ne</tt><a class="headerlink" href="#2to3fixer-ne" title="Permalink to this definition">¶</a></dt>
<dd>Converts the old not-equal syntax, <tt class="docutils literal"><span class="pre"><></span></tt>, to <tt class="docutils literal"><span class="pre">!=</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-next">
<tt class="descname">next</tt><a class="headerlink" href="#2to3fixer-next" title="Permalink to this definition">¶</a></dt>
<dd>Converts the use of iterator’s <a title="iterator.next" class="reference external" href="stdtypes.html#iterator.next"><tt class="xref docutils literal"><span class="pre">next()</span></tt></a> methods to the
<a title="next" class="reference external" href="functions.html#next"><tt class="xref docutils literal"><span class="pre">next()</span></tt></a> function. It also renames <a title="next" class="reference external" href="functions.html#next"><tt class="xref docutils literal"><span class="pre">next()</span></tt></a> methods to
<tt class="xref docutils literal"><span class="pre">__next__()</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-nonzero">
<tt class="descname">nonzero</tt><a class="headerlink" href="#2to3fixer-nonzero" title="Permalink to this definition">¶</a></dt>
<dd>Renames <a title="object.__nonzero__" class="reference external" href="../reference/datamodel.html#object.__nonzero__"><tt class="xref docutils literal"><span class="pre">__nonzero__()</span></tt></a> to <tt class="xref docutils literal"><span class="pre">__bool__()</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-numliterals">
<tt class="descname">numliterals</tt><a class="headerlink" href="#2to3fixer-numliterals" title="Permalink to this definition">¶</a></dt>
<dd>Converts octal literals into the new syntax.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-paren">
<tt class="descname">paren</tt><a class="headerlink" href="#2to3fixer-paren" title="Permalink to this definition">¶</a></dt>
<dd>Add extra parenthesis where they are required in list comprehensions. For
example, <tt class="docutils literal"><span class="pre">[x</span> <span class="pre">for</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">1,</span> <span class="pre">2]</span></tt> becomes <tt class="docutils literal"><span class="pre">[x</span> <span class="pre">for</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">(1,</span> <span class="pre">2)]</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-print">
<tt class="descname">print</tt><a class="headerlink" href="#2to3fixer-print" title="Permalink to this definition">¶</a></dt>
<dd>Converts the <a class="reference external" href="../reference/simple_stmts.html#print"><tt class="xref docutils literal"><span class="pre">print</span></tt></a> statement to the <a title="print" class="reference external" href="functions.html#print"><tt class="xref docutils literal"><span class="pre">print()</span></tt></a> function.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-raise">
<tt class="descname">raise</tt><a class="headerlink" href="#2to3fixer-raise" title="Permalink to this definition">¶</a></dt>
<dd>Converts <tt class="docutils literal"><span class="pre">raise</span> <span class="pre">E,</span> <span class="pre">V</span></tt> to <tt class="docutils literal"><span class="pre">raise</span> <span class="pre">E(V)</span></tt>, and <tt class="docutils literal"><span class="pre">raise</span> <span class="pre">E,</span> <span class="pre">V,</span> <span class="pre">T</span></tt> to <tt class="docutils literal"><span class="pre">raise</span>
<span class="pre">E(V).with_traceback(T)</span></tt>. If <tt class="docutils literal"><span class="pre">E</span></tt> is a tuple, the translation will be
incorrect because substituting tuples for exceptions has been removed in 3.0.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-raw_input">
<tt class="descname">raw_input</tt><a class="headerlink" href="#2to3fixer-raw_input" title="Permalink to this definition">¶</a></dt>
<dd>Converts <a title="raw_input" class="reference external" href="functions.html#raw_input"><tt class="xref docutils literal"><span class="pre">raw_input()</span></tt></a> to <a title="input" class="reference external" href="functions.html#input"><tt class="xref docutils literal"><span class="pre">input()</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-reduce">
<tt class="descname">reduce</tt><a class="headerlink" href="#2to3fixer-reduce" title="Permalink to this definition">¶</a></dt>
<dd>Handles the move of <a title="reduce" class="reference external" href="functions.html#reduce"><tt class="xref docutils literal"><span class="pre">reduce()</span></tt></a> to <a title="functools.reduce" class="reference external" href="functools.html#functools.reduce"><tt class="xref docutils literal"><span class="pre">functools.reduce()</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-renames">
<tt class="descname">renames</tt><a class="headerlink" href="#2to3fixer-renames" title="Permalink to this definition">¶</a></dt>
<dd>Changes <a title="sys.maxint" class="reference external" href="sys.html#sys.maxint"><tt class="xref docutils literal"><span class="pre">sys.maxint</span></tt></a> to <a title="sys.maxsize" class="reference external" href="sys.html#sys.maxsize"><tt class="xref docutils literal"><span class="pre">sys.maxsize</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-repr">
<tt class="descname">repr</tt><a class="headerlink" href="#2to3fixer-repr" title="Permalink to this definition">¶</a></dt>
<dd>Replaces backtick repr with the <a title="repr" class="reference external" href="functions.html#repr"><tt class="xref docutils literal"><span class="pre">repr()</span></tt></a> function.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-set_literal">
<tt class="descname">set_literal</tt><a class="headerlink" href="#2to3fixer-set_literal" title="Permalink to this definition">¶</a></dt>
<dd>Replaces use of the <a title="set" class="reference external" href="stdtypes.html#set"><tt class="xref docutils literal"><span class="pre">set</span></tt></a> constructor with set literals. This fixer
is optional.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-standard_error">
<tt class="descname">standard_error</tt><a class="headerlink" href="#2to3fixer-standard_error" title="Permalink to this definition">¶</a></dt>
<dd>Renames <a title="exceptions.StandardError" class="reference external" href="exceptions.html#exceptions.StandardError"><tt class="xref docutils literal"><span class="pre">StandardError</span></tt></a> to <a title="exceptions.Exception" class="reference external" href="exceptions.html#exceptions.Exception"><tt class="xref docutils literal"><span class="pre">Exception</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-sys_exc">
<tt class="descname">sys_exc</tt><a class="headerlink" href="#2to3fixer-sys_exc" title="Permalink to this definition">¶</a></dt>
<dd>Changes the deprecated <a title="sys.exc_value" class="reference external" href="sys.html#sys.exc_value"><tt class="xref docutils literal"><span class="pre">sys.exc_value</span></tt></a>, <a title="sys.exc_type" class="reference external" href="sys.html#sys.exc_type"><tt class="xref docutils literal"><span class="pre">sys.exc_type</span></tt></a>,
<a title="sys.exc_traceback" class="reference external" href="sys.html#sys.exc_traceback"><tt class="xref docutils literal"><span class="pre">sys.exc_traceback</span></tt></a> to use <a title="sys.exc_info" class="reference external" href="sys.html#sys.exc_info"><tt class="xref docutils literal"><span class="pre">sys.exc_info()</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-throw">
<tt class="descname">throw</tt><a class="headerlink" href="#2to3fixer-throw" title="Permalink to this definition">¶</a></dt>
<dd>Fixes the API change in generator’s <tt class="xref docutils literal"><span class="pre">throw()</span></tt> method.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-tuple_params">
<tt class="descname">tuple_params</tt><a class="headerlink" href="#2to3fixer-tuple_params" title="Permalink to this definition">¶</a></dt>
<dd>Removes implicit tuple parameter unpacking. This fixer inserts temporary
variables.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-types">
<tt class="descname">types</tt><a class="headerlink" href="#2to3fixer-types" title="Permalink to this definition">¶</a></dt>
<dd>Fixes code broken from the removal of some members in the <a title="Names for built-in types." class="reference external" href="types.html#module-types"><tt class="xref docutils literal"><span class="pre">types</span></tt></a>
module.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-unicode">
<tt class="descname">unicode</tt><a class="headerlink" href="#2to3fixer-unicode" title="Permalink to this definition">¶</a></dt>
<dd>Renames <a title="unicode" class="reference external" href="functions.html#unicode"><tt class="xref docutils literal"><span class="pre">unicode</span></tt></a> to <a title="str" class="reference external" href="functions.html#str"><tt class="xref docutils literal"><span class="pre">str</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-urllib">
<tt class="descname">urllib</tt><a class="headerlink" href="#2to3fixer-urllib" title="Permalink to this definition">¶</a></dt>
<dd>Handles the rename of <a title="Open an arbitrary network resource by URL (requires sockets)." class="reference external" href="urllib.html#module-urllib"><tt class="xref docutils literal"><span class="pre">urllib</span></tt></a> and <a title="Next generation URL opening library." class="reference external" href="urllib2.html#module-urllib2"><tt class="xref docutils literal"><span class="pre">urllib2</span></tt></a> to the <a title="Open an arbitrary network resource by URL (requires sockets)." class="reference external" href="urllib.html#module-urllib"><tt class="xref docutils literal"><span class="pre">urllib</span></tt></a>
package.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-ws_comma">
<tt class="descname">ws_comma</tt><a class="headerlink" href="#2to3fixer-ws_comma" title="Permalink to this definition">¶</a></dt>
<dd>Removes excess whitespace from comma separated items. This fixer is
optional.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-xrange">
<tt class="descname">xrange</tt><a class="headerlink" href="#2to3fixer-xrange" title="Permalink to this definition">¶</a></dt>
<dd>Renames <a title="xrange" class="reference external" href="functions.html#xrange"><tt class="xref docutils literal"><span class="pre">xrange()</span></tt></a> to <a title="range" class="reference external" href="functions.html#range"><tt class="xref docutils literal"><span class="pre">range()</span></tt></a> and wraps existing <a title="range" class="reference external" href="functions.html#range"><tt class="xref docutils literal"><span class="pre">range()</span></tt></a>
calls with <a title="list" class="reference external" href="functions.html#list"><tt class="xref docutils literal"><span class="pre">list</span></tt></a>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-xreadlines">
<tt class="descname">xreadlines</tt><a class="headerlink" href="#2to3fixer-xreadlines" title="Permalink to this definition">¶</a></dt>
<dd>Changes <tt class="docutils literal"><span class="pre">for</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">file.xreadlines()</span></tt> to <tt class="docutils literal"><span class="pre">for</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">file</span></tt>.</dd></dl>
<dl class="2to3fixer">
<dt id="2to3fixer-zip">
<tt class="descname">zip</tt><a class="headerlink" href="#2to3fixer-zip" title="Permalink to this definition">¶</a></dt>
<dd>Wraps <a title="zip" class="reference external" href="functions.html#zip"><tt class="xref docutils literal"><span class="pre">zip()</span></tt></a> usage in a <a title="list" class="reference external" href="functions.html#list"><tt class="xref docutils literal"><span class="pre">list</span></tt></a> call. This is disabled when
<tt class="docutils literal"><span class="pre">from</span> <span class="pre">future_builtins</span> <span class="pre">import</span> <span class="pre">zip</span></tt> appears.</dd></dl>
</div>
<div class="section" id="module-lib2to3">
<h2>25.4.3. <tt class="xref docutils literal"><span class="pre">lib2to3</span></tt> - 2to3’s library<a class="headerlink" href="#module-lib2to3" title="Permalink to this headline">¶</a></h2>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The <tt class="xref docutils literal"><span class="pre">lib2to3</span></tt> API should be considered unstable and may change
drastically in the future.</p>
</div>
</div>
</div>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference external" href="#">25.4. 2to3 - Automated Python 2 to 3 code translation</a><ul>
<li><a class="reference external" href="#using-2to3">25.4.1. Using 2to3</a></li>
<li><a class="reference external" href="#fixers">25.4.2. Fixers</a></li>
<li><a class="reference external" href="#module-lib2to3">25.4.3. <tt class="docutils literal"><span class="pre">lib2to3</span></tt> - 2to3’s library</a></li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
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