我正在尝试构建具有两个损失函数的神经网络，这些函数像加权总和一样组合在一起。第一个简单地计算密集层和给定标签的线性输出mean square error，但是另一个大量使用嵌套的tf.map_fn。有与tf.layers.batch_normalization()一起使用的批处理规范层，因此我不得不将这些行添加到优化目标中：
with tf.name_scope("Optimizer"):
with tf.control_dependencies(tf.get_collection(tf.GraphKeys.UPDATE_OPS)):
adam = tf.train.AdamOptimizer()
self.train_op = adam.minimize(self.total_loss)
但是我得到错误：
AttributeError: 'NoneType' object has no attribute 'op'
它来自minimize()方法。如果我删除控件依赖项，则没有错误。另外，如果我删除依赖于循环的第二个优化目标，则没有错误。我已经测试了正向传播中的第二损失函数，它工作得很好。
任何想法如何跟踪问题？完整的错误日志：
Traceback (most recent call last):
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 3267, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)
File "<ipython-input-2-6d5efdb6d091>", line 1, in <module>
runfile('/home/mtarasov/PycharmProjects/ML/src/utils/model.py', wdir='/home/mtarasov/PycharmProjects/ML/src/utils')
File "/home/mtarasov/Installations/pycharm-2018.2.4/helpers/pydev/_pydev_bundle/pydev_umd.py", line 198, in runfile
pydev_imports.execfile(filename, global_vars, local_vars) # execute the script
File "/home/mtarasov/Installations/pycharm-2018.2.4/helpers/pydev/_pydev_imps/_pydev_execfile.py", line 18, in execfile
exec(compile(contents+"\n", file, 'exec'), glob, loc)
File "/home/mtarasov/PycharmProjects/ML/src/utils/model.py", line 168, in <module>
model = Model().build()
File "/home/mtarasov/PycharmProjects/ML/src/utils/model.py", line 60, in build
self.train_op = adam.minimize(self.total_loss)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/training/optimizer.py", line 400, in minimize
grad_loss=grad_loss)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/training/optimizer.py", line 514, in compute_gradients
colocate_gradients_with_ops=colocate_gradients_with_ops)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/gradients_impl.py", line 596, in gradients
gate_gradients, aggregation_method, stop_gradients)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/gradients_impl.py", line 663, in _GradientsHelper
to_ops, from_ops, colocate_gradients_with_ops, func_graphs, xs)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/gradients_impl.py", line 190, in _PendingCount
between_op_list, between_ops, colocate_gradients_with_ops)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 1432, in MaybeCreateControlFlowState
loop_state.AddWhileContext(op, between_op_list, between_ops)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 1244, in AddWhileContext
grad_state = GradLoopState(forward_ctxt, outer_grad_state)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 846, in __init__
real_cnt, outer_grad_state)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 2585, in AddBackpropLoopCounter
name="b_count")
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 248, in _Enter
data, frame_name, is_constant, parallel_iterations, name=name)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/gen_control_flow_ops.py", line 178, in enter
parallel_iterations=parallel_iterations, name=name)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/framework/op_def_library.py", line 787, in _apply_op_helper
op_def=op_def)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/util/deprecation.py", line 454, in new_func
return func(*args, **kwargs)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 3155, in create_op
op_def=op_def)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 1746, in __init__
self._control_flow_post_processing()
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 1757, in _control_flow_post_processing
self._control_flow_context.AddOp(self)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 2438, in AddOp
self._AddOpInternal(op)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 2475, in _AddOpInternal
for x in external_inputs if x.outputs]
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 2475, in <listcomp>
for x in external_inputs if x.outputs]
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/array_ops.py", line 80, in identity
return gen_array_ops.identity(input, name=name)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/gen_array_ops.py", line 3264, in identity
"Identity", input=input, name=name)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/framework/op_def_library.py", line 787, in _apply_op_helper
op_def=op_def)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/util/deprecation.py", line 454, in new_func
return func(*args, **kwargs)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 3155, in create_op
op_def=op_def)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 1746, in __init__
self._control_flow_post_processing()
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 1757, in _control_flow_post_processing
self._control_flow_context.AddOp(self)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 2438, in AddOp
self._AddOpInternal(op)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 2466, in _AddOpInternal
self._MaybeAddControlDependency(op)
File "/home/mtarasov/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 2504, in _MaybeAddControlDependency
op._add_control_input(self.GetControlPivot().op)
AttributeError: 'NoneType' object has no attribute 'op
参考方案
加上mcstarioni的答案。如前所述，用tf.keras.layers.BatchNormalization替换批处理规范层似乎可以消除该错误。但是，这是因为keras中的BatchNormalization不会像here所示那样在UPDATE_OPS中添加批处理规范参数，因为它使用了不同的训练方式。如果检查移动平均值和方差，您会注意到在训练过程中仅通过运行train_op并不会更新它们。除了layer.update以外，还必须运行train_op，这应该可以解决问题。
或者，如果可能，请尝试删除嵌套的map_fn。
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