Provide a simple example of your code, and what it does.  Describe the
python version and OS platform you're running it on.  And detail the
contents of any extra files or environment values that are needed to
reproduce the problem.

(You may find http://www.catb.org/~esr/faqs/smart-questions.html  useful)

BTW, I don't know of any method __import__(), only a builtin function,
so I don't see how you can overload it. But your example should make it
clear what you really meant.

py> import __builtin__
py> builtin_import = __builtin__.__import__
py> def __import__(*args):
...   module = builtin_import(*args)
...   module.__signature__ = "kilroywashere"
...   return module
...
py> __builtin__.__import__ = __import__
py>
py> import htmllib
py> dir(htmllib)
['AS_IS', 'HTMLParseError', 'HTMLParser', '__all__', '__builtins__',
  '__doc__', '__file__', '__name__', '__package__', '__signature__',
  'sgmllib', 'test']
py> htmllib.__signature__
'kilroywashere'