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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 watch(self, *keys):
 """ Put the pipeline into immediate execution mode. Does not actually watch any keys. """

        if self.explicit_transaction:
            raise RedisError("Cannot issue a WATCH after a MULTI")
        self.watching = True
        for key in keys:
            self._watched_keys[key] = deepcopy(self.mock_redis.redis.get(self.mock_redis._encode(key)))