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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 ancestor(self, value):
 """Set the ancestor for the query :type value: :class:`~google.cloud.datastore.key.Key` :param value: the new ancestor key """

        if not isinstance(value, Key):
            raise TypeError("Ancestor must be a Key")
        self._ancestor = value