The problem is that in the decorator, you just get the compiled function. So you can modify the bytecode but not operate on the AST anymore.

I thought about this and wrote a patch for CPython that it also stores the original AST of any compiled function in the function object.

Some discussion about this:

http://thread.gmane.org/gmane.comp.python.devel/126754

http://thread.gmane.org/gmane.comp.python.devel/126760

You can find the line number that the func was defined in and reparse the source. I do this in quite a few decorators that need source.

The other option is to wrap the thing decorated in a doc string

    @fancy_source_needing_decorator
    def foo(s):
        """
        put some haskell or DSL stuff in here
        """

Then you don't have to reparse the source, etc etc, but it still gets packaged as a function.

Would you mind linking to some examples? I'd love to read them.

I remember this being used in a unit testing framework of some sort.. maybe twisted's?