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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_load_from(self, load_from):
 """Update load_from in Cache and backend."""

        assert load_from is None or isinstance(load_from, Cache), \
            "load_from needs to be None or a Cache object."
        assert load_from is None or load_from.cl_size <= self.cl_size, \
            "cl_size may only increase towards main memory."
        self.load_from = load_from
        self.backend.load_from = load_from.backend