以下是我完整代码的链接：
https://github.com/roshanDD/YAD2K/blob/master/yad2k/models/keras_yolo.py#L253
我只想打印出名为true_areas的张量的值。我运行了以下代码：
sess = tf.InteractiveSession()true_areas = true_wh[..., 0] * true_wh[..., 1]tf.Print(true_areas, [true_areas], message = "This is True Areas: ")b = tf.add(true_areas, true_areas).eval()但它返回了以下错误：
Caused by op 'input_2', defined at: File "learning.py", line 358, in <module> _main(args) File "learning.py", line 66, in _main model_body, model = create_model(anchors, class_names) File "learning.py", line 185, in create_model boxes_input = Input(shape=(None, 5)) File "/home/ubuntu/anaconda2/envs/py35/lib/python3.5/site-packages/keras/engine/topology.py", line 1388, in Input input_tensor=tensor) File "/home/ubuntu/anaconda2/envs/py35/lib/python3.5/site-packages/keras/engine/topology.py", line 1299, in __init__ name=self.name) File "/home/ubuntu/anaconda2/envs/py35/lib/python3.5/site-packages/keras/backend/tensorflow_backend.py", line 349, in placeholder x = tf.placeholder(dtype, shape=shape, name=name) File "/home/ubuntu/anaconda2/envs/py35/lib/python3.5/site-packages/tensorflow/python/ops/array_ops.py", line 1507, in placeholder name=name) File "/home/ubuntu/anaconda2/envs/py35/lib/python3.5/site-packages/tensorflow/python/ops/gen_array_ops.py", line 1997, in _placeholder name=name) File "/home/ubuntu/anaconda2/envs/py35/lib/python3.5/site-packages/tensorflow/python/framework/op_def_library.py", line 768, in apply_op op_def=op_def) File "/home/ubuntu/anaconda2/envs/py35/lib/python3.5/site-packages/tensorflow/python/framework/ops.py", line 2336, in create_op original_op=self._default_original_op, op_def=op_def) File "/home/ubuntu/anaconda2/envs/py35/lib/python3.5/site-packages/tensorflow/python/framework/ops.py", line 1228, in __init__ self._traceback = _extract_stack()InvalidArgumentError (see above for traceback): You must feed a value for placeholder tensor 'input_2' with dtype float [[Node: input_2 = Placeholder[dtype=DT_FLOAT, shape=[], _device="/job:localhost/replica:0/task:0/cpu:0"]()]]它提到的那个占位符是什么？
回答：
错误消息告诉你，你的代码中某个地方定义了一个名为input_2的tf.placeholder()。
当你想要评估依赖于这个占位符的图时，你需要提供值给这个占位符。应该看起来像这样：
b = tf.add(true_areas, true_areas).eval({input_2: someInputValues})