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1class 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 delegator 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
31if __name__ == '__main__':
32    from unittest import main
33    main('idlelib.idle_test.test_delegator', verbosity=2)
34