TensorFlow：TypeError：不允许将tf.Tensor作为Python bool使用

Question

我正在尝试使用CNN输出中的描述符来定义三重态损失，但是当我尝试训练网络时会出现此错误。

我对损失函数的定义：

def compute_loss(descriptor, margin):
    diff_pos = descriptor[0:1800:3] - descriptor[1:1800:3]
    diff_neg = descriptor[0:1800:3] - descriptor[2:1800:3]
    Ltriplet = np.maximum(0, 1 - tf.square(diff_neg)/(tf.square(diff_pos) + margin))
    Lpair = tf.square(diff_pos)

    Loss = Ltriplet + Lpair

    return Loss

这里的描述子是CNN的结果，CNN的收入是一组三重集合，包含按此顺序准确的锚，拉和推。输入时，我将600个三元组打包在一起，并将其输入到CNN中。

然后在训练网络时出现此错误：

2018-03-08 16:40:49.529263: I tensorflow/core/platform/cpu_feature_guard.cc:140] Your CPU supports instructions that this TensorFlow binary was not compiled to use: AVX2 FMA
Traceback (most recent call last):
  File "/Users/gaoyingqiang/Documents/GitHub/Master-TUM/TDCV/exercise_3/ex3/task2_new.py", line 78, in <module>
    loss = compute_loss(h_fc2, margin)
  File "/Users/gaoyingqiang/Documents/GitHub/Master-TUM/TDCV/exercise_3/ex3/task2_new.py", line 37, in compute_loss
    Ltriplet = np.maximum(0, 1 - tf.square(diff_neg)/(tf.square(diff_pos) + margin))
  File "/Users/gaoyingqiang/.virtualenvs/ex3/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 614, in __bool__
    raise TypeError("Using a `tf.Tensor` as a Python `bool` is not allowed. "
TypeError: Using a `tf.Tensor` as a Python `bool` is not allowed. Use `if t is not None:` instead of `if t:` to test if a tensor is defined, and use TensorFlow ops such as tf.cond to execute subgraphs conditioned on the value of a tensor.

Process finished with exit code 1

哪里出问题了？

Answer 1

您正在混合numpy和tensorflow操作。Tensorflow通常接受numpy数组（它们的值是静态已知的，因此可以转换为常量），反之则不然（仅在运行会话时才知道张量值，但急切的评估除外）。

解决方案：更改np.maximum为tf.maximum。