## 31.3.3 Examples

This section shows several simple examples of ASTs for Python source code. The examples demonstrate how to use the `parse()` function, what the repr of an AST looks like, and how to access attributes of an AST node.

The first module defines a single function. Assume it is stored in /tmp/doublelib.py.

    """This is an example module.

    This is the docstring.
    """

    def double(x):
        "Return twice the argument"
        return x * 2

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 `compiler.ast` module.

    >>> 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))))])