Callable modules?

[Paul Rubin]

I seem to remember seeing something somewhere about making a module
callable, but I can't seem to find it in the docs.  Basically I want
to have a file foo.py, and be able to say (in another file):

  import foo
  x = foo(3)

instead of having to say foo.mumble(3).

Is there a way to do that?  I tried putting

  def __call__(x): ...

into foo.py but that didn't work.  

If there's not a way to do this already, maybe it's a reasonable
addition.