Edit File: codeop.html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>28.2. codeop — Compile Python code — Python v2.6.6 documentation</title> <link rel="stylesheet" href="../_static/default.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '2.6.6', COLLAPSE_MODINDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python v2.6.6 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="top" title="Python v2.6.6 documentation" href="../index.html" /> <link rel="up" title="28. 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Custom Python Interpreters</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="module-codeop"> <h1>28.2. <tt class="xref docutils literal"><span class="pre">codeop</span></tt> — Compile Python code<a class="headerlink" href="#module-codeop" title="Permalink to this headline">¶</a></h1> <p>The <tt class="xref docutils literal"><span class="pre">codeop</span></tt> module provides utilities upon which the Python read-eval-print loop can be emulated, as is done in the <a title="Facilities to implement read-eval-print loops." class="reference external" href="code.html#module-code"><tt class="xref docutils literal"><span class="pre">code</span></tt></a> module. As a result, you probably don’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 title="Facilities to implement read-eval-print loops." class="reference external" href="code.html#module-code"><tt class="xref 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 ‘<tt class="docutils literal"><span class="pre">>>></span></tt>‘ or ‘<tt class="docutils literal"><span class="pre">...</span></tt>‘ 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 <tt class="xref docutils literal"><span class="pre">codeop</span></tt> 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">'<input>'</span></tt>. Returns <tt class="xref 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 title="exceptions.SyntaxError" class="reference external" href="exceptions.html#exceptions.SyntaxError"><tt class="xref docutils literal"><span class="pre">SyntaxError</span></tt></a> is raised if there is invalid Python syntax, and <a title="exceptions.OverflowError" class="reference external" href="exceptions.html#exceptions.OverflowError"><tt class="xref docutils literal"><span class="pre">OverflowError</span></tt></a> or <a title="exceptions.ValueError" class="reference external" href="exceptions.html#exceptions.ValueError"><tt class="xref 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 external" href="../glossary.html#term-expression"><em class="xref">expression</em></a> (<tt class="docutils literal"><span class="pre">'eval'</span></tt>). Any other value will cause <a title="exceptions.ValueError" class="reference external" href="exceptions.html#exceptions.ValueError"><tt class="xref 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>Instances of this class have <a title="object.__call__" class="reference external" href="../reference/datamodel.html#object.__call__"><tt class="xref docutils literal"><span class="pre">__call__()</span></tt></a> methods identical in signature to the built-in function <a title="compile" class="reference external" href="functions.html#compile"><tt class="xref docutils literal"><span class="pre">compile()</span></tt></a>, but with the difference that if the instance compiles program text containing a <a title="Future statement definitions" class="reference external" href="__future__.html#module-__future__"><tt class="xref docutils literal"><span class="pre">__future__</span></tt></a> statement, the instance ‘remembers’ and compiles all subsequent program texts with the statement in force.</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>Instances of this class have <a title="object.__call__" class="reference external" href="../reference/datamodel.html#object.__call__"><tt class="xref docutils literal"><span class="pre">__call__()</span></tt></a> methods identical in signature to <a title="codeop.compile_command" class="reference internal" href="#codeop.compile_command"><tt class="xref 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 ‘remembers’ and compiles all subsequent program texts with the statement in force.</dd></dl> <p>A note on version compatibility: the <a title="codeop.Compile" class="reference internal" href="#codeop.Compile"><tt class="xref docutils literal"><span class="pre">Compile</span></tt></a> and <a title="codeop.CommandCompiler" class="reference internal" href="#codeop.CommandCompiler"><tt class="xref 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> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h4>Previous topic</h4> <p class="topless"><a href="code.html" title="previous chapter">28.1. <tt class="docutils literal docutils literal"><span class="pre">code</span></tt> — Interpreter base classes</a></p> <h4>Next topic</h4> <p class="topless"><a href="restricted.html" title="next chapter">29. 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