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  <div class="section" id="module-codeop">
<span id="codeop-compile-python-code"></span><h1>28.2. <a class="reference internal" href="#module-codeop" title="codeop: Compile (possibly incomplete) Python code."><tt class="xref py py-mod docutils literal"><span class="pre">codeop</span></tt></a> &#8212; Compile Python code<a class="headerlink" href="#module-codeop" title="Permalink to this headline">¶</a></h1>
<p>The <a class="reference internal" href="#module-codeop" title="codeop: Compile (possibly incomplete) Python code."><tt class="xref py py-mod docutils literal"><span class="pre">codeop</span></tt></a> module provides utilities upon which the Python
read-eval-print loop can be emulated, as is done in the <a class="reference internal" href="code.html#module-code" title="code: Facilities to implement read-eval-print loops."><tt class="xref py py-mod docutils literal"><span class="pre">code</span></tt></a> module.  As
a result, you probably don&#8217;t want to use the module directly; if you want to
include such a loop in your program you probably want to use the <a class="reference internal" href="code.html#module-code" title="code: Facilities to implement read-eval-print loops."><tt class="xref py py-mod docutils literal"><span class="pre">code</span></tt></a>
module instead.</p>
<p>There are two parts to this job:</p>
<ol class="arabic simple">
<li>Being able to tell if a line of input completes a Python  statement: in
short, telling whether to print &#8216;<tt class="docutils literal"><span class="pre">&gt;&gt;&gt;</span></tt>&#8216; or &#8216;<tt class="docutils literal"><span class="pre">...</span></tt>&#8216; next.</li>
<li>Remembering which future statements the user has entered, so  subsequent
input can be compiled with these in effect.</li>
</ol>
<p>The <a class="reference internal" href="#module-codeop" title="codeop: Compile (possibly incomplete) Python code."><tt class="xref py py-mod docutils literal"><span class="pre">codeop</span></tt></a> module provides a way of doing each of these things, and a way
of doing them both.</p>
<p>To do just the former:</p>
<dl class="function">
<dt id="codeop.compile_command">
<tt class="descclassname">codeop.</tt><tt class="descname">compile_command</tt><big>(</big><em>source</em><span class="optional">[</span>, <em>filename</em><span class="optional">[</span>, <em>symbol</em><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#codeop.compile_command" title="Permalink to this definition">¶</a></dt>
<dd><p>Tries to compile <em>source</em>, which should be a string of Python code and return a
code object if <em>source</em> is valid Python code. In that case, the filename
attribute of the code object will be <em>filename</em>, which defaults to
<tt class="docutils literal"><span class="pre">'&lt;input&gt;'</span></tt>. Returns <tt class="docutils literal"><span class="pre">None</span></tt> if <em>source</em> is <em>not</em> valid Python code, but is a
prefix of valid Python code.</p>
<p>If there is a problem with <em>source</em>, an exception will be raised.
<a class="reference internal" href="exceptions.html#exceptions.SyntaxError" title="exceptions.SyntaxError"><tt class="xref py py-exc docutils literal"><span class="pre">SyntaxError</span></tt></a> is raised if there is invalid Python syntax, and
<a class="reference internal" href="exceptions.html#exceptions.OverflowError" title="exceptions.OverflowError"><tt class="xref py py-exc docutils literal"><span class="pre">OverflowError</span></tt></a> or <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> if there is an invalid literal.</p>
<p>The <em>symbol</em> argument determines whether <em>source</em> is compiled as a statement
(<tt class="docutils literal"><span class="pre">'single'</span></tt>, the default) or as an <a class="reference internal" href="../glossary.html#term-expression"><em class="xref std std-term">expression</em></a> (<tt class="docutils literal"><span class="pre">'eval'</span></tt>).  Any
other value will cause <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> to  be raised.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">It is possible (but not likely) that the parser stops parsing with a
successful outcome before reaching the end of the source; in this case,
trailing symbols may be ignored instead of causing an error.  For example,
a backslash followed by two newlines may be followed by arbitrary garbage.
This will be fixed once the API for the parser is better.</p>
</div>
</dd></dl>

<dl class="class">
<dt id="codeop.Compile">
<em class="property">class </em><tt class="descclassname">codeop.</tt><tt class="descname">Compile</tt><a class="headerlink" href="#codeop.Compile" title="Permalink to this definition">¶</a></dt>
<dd><p>Instances of this class have <a class="reference internal" href="../reference/datamodel.html#object.__call__" title="object.__call__"><tt class="xref py py-meth docutils literal"><span class="pre">__call__()</span></tt></a> methods identical in signature to
the built-in function <a class="reference internal" href="functions.html#compile" title="compile"><tt class="xref py py-func docutils literal"><span class="pre">compile()</span></tt></a>, but with the difference that if the
instance compiles program text containing a <a class="reference internal" href="__future__.html#module-__future__" title="__future__: Future statement definitions"><tt class="xref py py-mod docutils literal"><span class="pre">__future__</span></tt></a> statement, the
instance &#8216;remembers&#8217; and compiles all subsequent program texts with the
statement in force.</p>
</dd></dl>

<dl class="class">
<dt id="codeop.CommandCompiler">
<em class="property">class </em><tt class="descclassname">codeop.</tt><tt class="descname">CommandCompiler</tt><a class="headerlink" href="#codeop.CommandCompiler" title="Permalink to this definition">¶</a></dt>
<dd><p>Instances of this class have <a class="reference internal" href="../reference/datamodel.html#object.__call__" title="object.__call__"><tt class="xref py py-meth docutils literal"><span class="pre">__call__()</span></tt></a> methods identical in signature to
<a class="reference internal" href="#codeop.compile_command" title="codeop.compile_command"><tt class="xref py py-func docutils literal"><span class="pre">compile_command()</span></tt></a>; the difference is that if the instance compiles program
text containing a <tt class="docutils literal"><span class="pre">__future__</span></tt> statement, the instance &#8216;remembers&#8217; and
compiles all subsequent program texts with the statement in force.</p>
</dd></dl>

<p>A note on version compatibility: the <a class="reference internal" href="#codeop.Compile" title="codeop.Compile"><tt class="xref py py-class docutils literal"><span class="pre">Compile</span></tt></a> and
<a class="reference internal" href="#codeop.CommandCompiler" title="codeop.CommandCompiler"><tt class="xref py py-class docutils literal"><span class="pre">CommandCompiler</span></tt></a> are new in Python 2.2.  If you want to enable the
future-tracking features of 2.2 but also retain compatibility with 2.1 and
earlier versions of Python you can either write</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">try</span><span class="p">:</span>
    <span class="kn">from</span> <span class="nn">codeop</span> <span class="kn">import</span> <span class="n">CommandCompiler</span>
    <span class="n">compile_command</span> <span class="o">=</span> <span class="n">CommandCompiler</span><span class="p">()</span>
    <span class="k">del</span> <span class="n">CommandCompiler</span>
<span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span>
    <span class="kn">from</span> <span class="nn">codeop</span> <span class="kn">import</span> <span class="n">compile_command</span>
</pre></div>
</div>
<p>which is a low-impact change, but introduces possibly unwanted global state into
your program, or you can write:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">try</span><span class="p">:</span>
    <span class="kn">from</span> <span class="nn">codeop</span> <span class="kn">import</span> <span class="n">CommandCompiler</span>
<span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span>
    <span class="k">def</span> <span class="nf">CommandCompiler</span><span class="p">():</span>
        <span class="kn">from</span> <span class="nn">codeop</span> <span class="kn">import</span> <span class="n">compile_command</span>
        <span class="k">return</span> <span class="n">compile_command</span>
</pre></div>
</div>
<p>and then call <tt class="docutils literal"><span class="pre">CommandCompiler</span></tt> every time you need a fresh compiler object.</p>
</div>


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