sam-t2/devtools/v9/html/python/lib/module-codeop.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<link rel="STYLESHEET" href="lib.css" type='text/css' />
<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
<link rel='start' href='../index.html' title='Python Documentation Index' />
<link rel="first" href="lib.html" title='Python Library Reference' />
<link rel='contents' href='contents.html' title="Contents" />
<link rel='index' href='genindex.html' title='Index' />
<link rel='last' href='about.html' title='About this document...' />
<link rel='help' href='about.html' title='About this document...' />
<link rel="next" href="module-pprint.html" />
<link rel="prev" href="module-code.html" />
<link rel="parent" href="python.html" />
<link rel="next" href="module-pprint.html" />
<meta name='aesop' content='information' />
<title>3.26 codeop -- Compile Python code</title>
</head>
<body>
<DIV CLASS="navigation">
<div id='top-navigation-panel' xml:id='top-navigation-panel'>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="3.25.2 Interactive Console Objects"
  href="console-objects.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="3. Python Runtime Services"
  href="python.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="3.27 pprint  "
  href="module-pprint.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="console-objects.html">3.25.2 Interactive Console Objects</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="python.html">3. Python Runtime Services</A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="module-pprint.html">3.27 pprint  </A>
</div>
<hr /></div>
</DIV>
<!--End of Navigation Panel-->

<H1><A NAME="SECTION0052600000000000000000">
3.26 <tt class="module">codeop</tt> --
         Compile Python code</A>
</H1>

<P>
<A NAME="module-codeop"></A>

<P>
The <tt class="module">codeop</tt> module provides utilities upon which the Python
read-eval-print loop can be emulated, as is done in the
<tt class="module"><a href="module-code.html">code</a></tt> 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 <tt class="module"><a href="module-code.html">code</a></tt> module instead.

<P>
There are two parts to this job:

<P>

<OL>
<LI>Being able to tell if a line of input completes a Python
        statement: in short, telling whether to print
        `<code>&gt;<code>&gt;</code>&gt;&nbsp;</code>' or `<code>...&nbsp;</code>' 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="module">codeop</tt> module provides a way of doing each of these
things, and a way of doing them both.

<P>
To do just the former:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-758' xml:id='l2h-758' class="function">compile_command</tt></b>(</nobr></td>
  <td><var>source</var><big>[</big><var>, filename</var><big>[</big><var>, symbol</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Tries to compile <var>source</var>, which should be a string of Python
code and return a code object if <var>source</var> is valid
Python code. In that case, the filename attribute of the code object
will be <var>filename</var>, which defaults to <code>'&lt;input&gt;'</code>.
Returns <code>None</code> if <var>source</var> is <em>not</em> valid Python
code, but is a prefix of valid Python code.

<P>
If there is a problem with <var>source</var>, an exception will be raised.
<tt class="exception">SyntaxError</tt> is raised if there is invalid Python syntax,
and <tt class="exception">OverflowError</tt> or <tt class="exception">ValueError</tt> if there is an
invalid literal.

<P>
The <var>symbol</var> argument determines whether <var>source</var> is compiled
as a statement (<code>'single'</code>, the default) or as an expression
(<code>'eval'</code>).  Any other value will cause <tt class="exception">ValueError</tt> to
be raised.

<P>
<strong>Caveat:</strong>
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.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-759' xml:id='l2h-759' class="class">Compile</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Instances of this class have <tt class="method">__call__()</tt> methods identical in
signature to the built-in function <tt class="function">compile()</tt>, but with the
difference that if the instance compiles program text containing a
<tt class="module">__future__</tt> statement, the instance 'remembers' and compiles
all subsequent program texts with the statement in force.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-760' xml:id='l2h-760' class="class">CommandCompiler</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Instances of this class have <tt class="method">__call__()</tt> methods identical in
signature to <tt class="function">compile_command()</tt>; the difference is that if
the instance compiles program text containing a <code>__future__</code>
statement, the instance 'remembers' and compiles all subsequent
program texts with the statement in force.
</dl>

<P>
A note on version compatibility: the <tt class="class">Compile</tt> and
<tt class="class">CommandCompiler</tt> 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="verbatim"><pre>
try:
    from codeop import CommandCompiler
    compile_command = CommandCompiler()
    del CommandCompiler
except ImportError:
    from codeop import compile_command
</pre></div>

<P>
which is a low-impact change, but introduces possibly unwanted global
state into your program, or you can write:

<P>
<div class="verbatim"><pre>
try:
    from codeop import CommandCompiler
except ImportError:
    def CommandCompiler():
        from codeop import compile_command
        return compile_command
</pre></div>

<P>
and then call <code>CommandCompiler</code> every time you need a fresh
compiler object.

<DIV CLASS="navigation">
<div class='online-navigation'>
<p></p><hr />
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="3.25.2 Interactive Console Objects"
  href="console-objects.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="3. Python Runtime Services"
  href="python.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="3.27 pprint  "
  href="module-pprint.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="console-objects.html">3.25.2 Interactive Console Objects</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="python.html">3. Python Runtime Services</A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="module-pprint.html">3.27 pprint  </A>
</div>
</div>
<hr />
<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
</DIV>
<!--End of Navigation Panel-->
<ADDRESS>
See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
</ADDRESS>
</BODY>
</HTML>