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class Delegator:
# The cache is only used to be able to change delegates!
def __init__(self, delegate=None):
self.delegate = delegate
self.__cache = set()
def __getattr__(self, name):
attr = getattr(self.delegate, name) # May raise AttributeError
setattr(self, name, attr)
self.__cache.add(name)
return attr
def __nonzero__(self):
# this is needed for PyPy: else, if self.delegate is None, the
# __getattr__ above picks NoneType.__nonzero__, which returns
# False. Thus, bool(Delegator()) is False as well, but it's not what
# we want. On CPython, bool(Delegator()) is True because NoneType
# does not have __nonzero__
return True
def resetcache(self):
for key in self.__cache:
try:
delattr(self, key)
except AttributeError:
pass
self.__cache.clear()
def setdelegate(self, delegate):
self.resetcache()
self.delegate = delegate
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