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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def set_cache_policy(self, func):
 """Set the context cache policy function. Args: func: A function that accepts a Key instance as argument and returns a bool indicating if it should be cached. May be None. """

    if func is None:
      func = self.default_cache_policy
    elif isinstance(func, bool):
      func = lambda unused_key, flag=func: flag
    self._cache_policy = func