Initializer for _tensor_name_to_ids.

    Returns:
      a {string: (int, int)}, mapping the name of tensor T to the index of T's
          operation in _operations and T's index in T's operation's outputs.

def _initialize_tensor_name_to_ids(self):
    """Initializer for _tensor_name_to_ids.

    Returns:
      a {string: (int, int)}, mapping the name of tensor T to the index of T's
          operation in _operations and T's index in T's operation's outputs.
    """
    tensor_name_to_ids = {}
    for i, operation in enumerate(self._operations):
      for j, tensor in enumerate(operation.outputs):
        tensor_name_to_ids[tensor.name] = (i, j)
    return tensor_name_to_ids