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<H2><A NAME="SECTION0021330000000000000000">
19.3.3 Examples</A>
</H2>
<P>
This section shows several simple examples of ASTs for Python source
code. The examples demonstrate how to use the <tt class="function">parse()</tt>
function, what the repr of an AST looks like, and how to access
attributes of an AST node.
<P>
The first module defines a single function. Assume it is stored in
<span class="file">/tmp/doublelib.py</span>.
<P>
<div class="verbatim"><pre>
"""This is an example module.
This is the docstring.
"""
def double(x):
"Return twice the argument"
return x * 2
</pre></div>
<P>
In the interactive interpreter session below, I have reformatted the
long AST reprs for readability. The AST reprs use unqualified class
names. If you want to create an instance from a repr, you must import
the class names from the <tt class="module">compiler.ast</tt> module.
<P>
<div class="verbatim"><pre>
>>> import compiler
>>> mod = compiler.parseFile("/tmp/doublelib.py")
>>> mod
Module('This is an example module.\n\nThis is the docstring.\n',
Stmt([Function(None, 'double', ['x'], [], 0,
'Return twice the argument',
Stmt([Return(Mul((Name('x'), Const(2))))]))]))
>>> from compiler.ast import *
>>> Module('This is an example module.\n\nThis is the docstring.\n',
... Stmt([Function(None, 'double', ['x'], [], 0,
... 'Return twice the argument',
... Stmt([Return(Mul((Name('x'), Const(2))))]))]))
Module('This is an example module.\n\nThis is the docstring.\n',
Stmt([Function(None, 'double', ['x'], [], 0,
'Return twice the argument',
Stmt([Return(Mul((Name('x'), Const(2))))]))]))
>>> mod.doc
'This is an example module.\n\nThis is the docstring.\n'
>>> for node in mod.node.nodes:
... print node
...
Function(None, 'double', ['x'], [], 0, 'Return twice the argument',
Stmt([Return(Mul((Name('x'), Const(2))))]))
>>> func = mod.node.nodes[0]
>>> func.code
Stmt([Return(Mul((Name('x'), Const(2))))])
</pre></div>
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<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
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