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      1 class Delegator:
      2 
      3     def __init__(self, delegate=None):
      4         self.delegate = delegate
      5         self.__cache = set()
      6         # Cache is used to only remove added attributes
      7         # when changing the delegate.
      8 
      9     def __getattr__(self, name):
     10         attr = getattr(self.delegate, name) # May raise AttributeError
     11         setattr(self, name, attr)
     12         self.__cache.add(name)
     13         return attr
     14 
     15     def resetcache(self):
     16         "Removes added attributes while leaving original attributes."
     17         # Function is really about resetting delagator dict
     18         # to original state.  Cache is just a means
     19         for key in self.__cache:
     20             try:
     21                 delattr(self, key)
     22             except AttributeError:
     23                 pass
     24         self.__cache.clear()
     25 
     26     def setdelegate(self, delegate):
     27         "Reset attributes and change delegate."
     28         self.resetcache()
     29         self.delegate = delegate
     30 
     31 if __name__ == '__main__':
     32     from unittest import main
     33     main('idlelib.idle_test.test_delegator', verbosity=2)
     34