examples/research_projects/bertabs/modeling_bertabs.py/TransformerDecoderState/_init_cache
class TransformerDecoderState:    def _init_cache(self, memory_bank, num_layers):
        self.cache = {}

        for l in range(num_layers):
            layer_cache = {"memory_keys": None, "memory_values": None}
            layer_cache["self_keys"] = None
            layer_cache["self_values"] = None
            self.cache["layer_{}".format(l)] = layer_cache