super_patch.py

import gc


def super_patch(old_obj, new_obj):
    if old_obj is new_obj:
        return
    gc.collect()
    for referrer_obj in gc.get_referrers(old_obj):
        if hasattr(referrer_obj, "iteritems"):
            for key, value in referrer_obj.iteritems():
                if value is old_obj:
                    referrer_obj[key] = new_obj

Python 2.7.5+ (default, Sep 19 2013, 13:48:49) 
[GCC 4.8.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from super_patch import super_patch
>>> from foouser import bar
>>> from foo import foo
>>> bar()
4
>>> super_patch(foo, lambda: 3)
>>> bar()
3
>>>