How to get the module from which the currently executing function was called?

This is my best solution so far to the problem of accessing the calling module from within a function:

import inspect
import sys
def calling_module(level=0):
    filename = inspect.stack()[level+2][1]
    modulename = inspect.getmodulename(filename)
    try:
        return sys.modules[modulename]
    except KeyError:
        return sys.modules['__main__']

...but implicit in the handling of the KeyError is the (largely unfounded) assumption that it can happen only if filename is being run as __main__.

Does the Python standard library provide a more robust way to do this?