Perhaps apigen.py can help: https://github.com/nipy/nipy/tree/master/tools.

This tool is described very briefly here: http://comments.gmane.org/gmane.comp.python.sphinx.devel/2912.

Or better yet, use pdoc.

Update: the sphinx-apidoc utility was added in Sphinx version 1.1.

pydoc is fantastic for generating documentation, but the documentation has to be written in the first place. You must have docstrings in your source code as was mentioned by RocketDonkey in the comments:

"""
This example module shows various types of documentation available for use
with pydoc.  To generate HTML documentation for this module issue the
command:

    pydoc -w foo

"""

class Foo(object):
    """
    Foo encapsulates a name and an age.
    """
    def __init__(self, name, age):
        """
        Construct a new 'Foo' object.

        :param name: The name of foo
        :param age: The ageof foo
        :return: returns nothing
        """
        self.name = name
        self.age = age

def bar(baz):
    """
    Prints baz to the display.
    """
    print baz

if __name__ == '__main__':
    f = Foo('John Doe', 42)
    bar("hello world")

The first docstring provides instructions for creating the documentation with pydoc. There are examples of different types of docstrings so you can see how they look when generated with pydoc.