utils.py 文件源码

def get_backward_ops(seed_tensors, treat_as_inputs=None):
    """
    Get backward ops from inputs to `seed_tensors` by topological order.

    :param seed_tensors: A Tensor or list of Tensors, for which to get all
        preceding Tensors.
    :param treat_as_inputs: None or a list of Tensors that is treated as
        inputs during the search (where to stop searching the backward graph).

    :return: A list of tensorflow `Operation` s in topological order.
    """
    if treat_as_inputs is None:
        treat_as_inputs = []
    treat_as_inputs = set(treat_as_inputs)
    if not isinstance(seed_tensors, (list, tuple)):
        seed_tensors = [seed_tensors]
    seed_tensors = [t for t in seed_tensors if t not in treat_as_inputs]
    seed_ops = list(OrderedDict.fromkeys(t.op for t in seed_tensors))
    q = deque(seed_ops)
    seen = set()
    done = set()
    ret = []
    while q:
        op = q[0]
        if op not in seen:
            seen.add(op)
            for tensor in reversed(op.inputs):
                if tensor not in treat_as_inputs:
                    q.appendleft(tensor.op)
            q.extendleft(reversed(op.control_inputs))
        else:
            # have seen this op before
            q.popleft()
            if op not in done:
                done.add(op)
                ret.append(op)
    return ret