class Delegator:

 def __init__(self, delegate=None):
 self.delegate = delegate
 self.__cache = set()
 # Cache is used to only remove added attributes
 # when changing the delegate.

 def __getattr__(self, name):
 attr = getattr(self.delegate, name) # May raise AttributeError
 setattr(self, name, attr)
 self.__cache.add(name)
 return attr

 def resetcache(self):
 "Removes added attributes while leaving original attributes."
 # Function is really about resetting delegator dict
 # to original state. Cache is just a means
 for key in self.__cache:
 try:
 delattr(self, key)
 except AttributeError:
 pass
 self.__cache.clear()

 def setdelegate(self, delegate):
 "Reset attributes and change delegate."
 self.resetcache()
 self.delegate = delegate

if __name__ == '__main__':
 from unittest import main
 main('idlelib.idle_test.test_delegator', verbosity=2)