我刚刚完成了 TensorFlow MNIST tutorial对于初学者。我在 Python 3 上的 Jupyter(本地安装)中运行最新版本的 TensorFlow。
我的代码如下，基本上是从教程中逐字提取的:
import tensorflow as tf
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
import argparse
import sys
from tensorflow.examples.tutorials.mnist import input_data
mnist = input_data.read_data_sets("MNIST_data/", one_hot=True)
x = tf.placeholder(tf.float32,[None,784])
W = tf.Variable(tf.zeros([784,10]))
b = tf.Variable(tf.zeros([10]))
y = tf.nn.softmax(tf.matmul(x,W)+b)
y_ = tf.placeholder(tf.float32,[None,10])
cross_entropy = tf.nn.softmax_cross_entropy_with_logits(labels=y_,logits=y)
sess= tf.InteractiveSession()
init = tf.global_variables_initializer()
sess.run(init)
train_step = tf.train.GradientDescentOptimizer(.05).minimize(cross_entropy)
for i in range(1000):
batch_x,batch_y = mnist.train.next_batch(100)
sess.run(train_step,feed_dict={x:batch_x,y:batch_y})
我认为问题可能出在 python3.因此，我尝试在 python 2.7 版本的 tensorflow 中运行相同的代码。没有改变。
---------------------------------------------------------------------------
InvalidArgumentError Traceback (most recent call last)
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/client/session.py in _do_call(self, fn, *args)
1138 try:
-> 1139 return fn(*args)
1140 except errors.OpError as e:
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/client/session.py in _run_fn(session, feed_dict, fetch_list, target_list, options, run_metadata)
1120 feed_dict, fetch_list, target_list,
-> 1121 status, run_metadata)
1122
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/contextlib.py in __exit__(self, type, value, traceback)
88 try:
---> 89 next(self.gen)
90 except StopIteration:
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/framework/errors_impl.py in raise_exception_on_not_ok_status()
465 compat.as_text(pywrap_tensorflow.TF_Message(status)),
--> 466 pywrap_tensorflow.TF_GetCode(status))
467 finally:
InvalidArgumentError: Shape [-1,10] has negative dimensions
[[Node: Placeholder_1 = Placeholder[dtype=DT_FLOAT, shape=[?,10], _device="/job:localhost/replica:0/task:0/cpu:0"]()]]
During handling of the above exception, another exception occurred:
InvalidArgumentError Traceback (most recent call last)
<ipython-input-10-89eb8cf9286c> in <module>()
1 for _ in range(1000):
2 batch_x,batch_y = mnist.train.next_batch(100)
----> 3 sess.run(train_step,feed_dict={x:batch_x,y:batch_y})
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/client/session.py in run(self, fetches, feed_dict, options, run_metadata)
787 try:
788 result = self._run(None, fetches, feed_dict, options_ptr,
--> 789 run_metadata_ptr)
790 if run_metadata:
791 proto_data = tf_session.TF_GetBuffer(run_metadata_ptr)
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/client/session.py in _run(self, handle, fetches, feed_dict, options, run_metadata)
995 if final_fetches or final_targets:
996 results = self._do_run(handle, final_targets, final_fetches,
--> 997 feed_dict_string, options, run_metadata)
998 else:
999 results = []
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/client/session.py in _do_run(self, handle, target_list, fetch_list, feed_dict, options, run_metadata)
1130 if handle is None:
1131 return self._do_call(_run_fn, self._session, feed_dict, fetch_list,
-> 1132 target_list, options, run_metadata)
1133 else:
1134 return self._do_call(_prun_fn, self._session, handle, feed_dict,
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/client/session.py in _do_call(self, fn, *args)
1150 except KeyError:
1151 pass
-> 1152 raise type(e)(node_def, op, message)
1153
1154 def _extend_graph(self):
InvalidArgumentError: Shape [-1,10] has negative dimensions
[[Node: Placeholder_1 = Placeholder[dtype=DT_FLOAT, shape=[?,10], _device="/job:localhost/replica:0/task:0/cpu:0"]()]]
Caused by op 'Placeholder_1', defined at:
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/runpy.py", line 193, in _run_module_as_main
"__main__", mod_spec)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/runpy.py", line 85, in _run_code
exec(code, run_globals)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/ipykernel_launcher.py", line 16, in <module>
app.launch_new_instance()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/traitlets/config/application.py", line 658, in launch_instance
app.start()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/ipykernel/kernelapp.py", line 477, in start
ioloop.IOLoop.instance().start()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/zmq/eventloop/ioloop.py", line 177, in start
super(ZMQIOLoop, self).start()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tornado/ioloop.py", line 888, in start
handler_func(fd_obj, events)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tornado/stack_context.py", line 277, in null_wrapper
return fn(*args, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/zmq/eventloop/zmqstream.py", line 440, in _handle_events
self._handle_recv()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/zmq/eventloop/zmqstream.py", line 472, in _handle_recv
self._run_callback(callback, msg)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/zmq/eventloop/zmqstream.py", line 414, in _run_callback
callback(*args, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tornado/stack_context.py", line 277, in null_wrapper
return fn(*args, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 283, in dispatcher
return self.dispatch_shell(stream, msg)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 235, in dispatch_shell
handler(stream, idents, msg)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 399, in execute_request
user_expressions, allow_stdin)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/ipykernel/ipkernel.py", line 196, in do_execute
res = shell.run_cell(code, store_history=store_history, silent=silent)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/ipykernel/zmqshell.py", line 533, in run_cell
return super(ZMQInteractiveShell, self).run_cell(*args, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 2698, in run_cell
interactivity=interactivity, compiler=compiler, result=result)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 2802, in run_ast_nodes
if self.run_code(code, result):
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 2862, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)
File "<ipython-input-4-c355762e89a9>", line 2, in <module>
y_ = tf.placeholder(tf.float32,[None,10])
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/ops/array_ops.py", line 1530, in placeholder
return gen_array_ops._placeholder(dtype=dtype, shape=shape, name=name)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/ops/gen_array_ops.py", line 1954, in _placeholder
name=name)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/framework/op_def_library.py", line 767, in apply_op
op_def=op_def)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 2506, in create_op
original_op=self._default_original_op, op_def=op_def)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 1269, in __init__
self._traceback = _extract_stack()
InvalidArgumentError (see above for traceback): Shape [-1,10] has negative dimensions
[[Node: Placeholder_1 = Placeholder[dtype=DT_FLOAT, shape=[?,10], _device="/job:localhost/replica:0/task:0/cpu:0"]()]]
有人可以告诉我我做错了什么吗？我认为修复本教程中的错误会很有用。
已解决!非常愚蠢的错误。在最后一行，我写了y，当我需要写y_的时候。如果有人能向我解释为什么这个错误会产生错误消息，我会很高兴。
请您参考如下方法:
产生这个错误的原因在于你这行代码中的一个类型:
sess.run(train_step,feed_dict={x:batch_x, y:batch_y})
你应该这样写:
sess.run(train_step,feed_dict={x:batch_x, y_:batch_y})
发生的情况是，您正在尝试将一批 100 个标签提供给一个 varibale，该 varibale 旨在保存单个值。
y 是您在此处实现的模型的输出:
y = tf.nn.softmax(tf.matmul(x,W)+b)
y_ 表示您首先为其创建占位符变量的大小为 [100,10] 的张量。对于每次训练迭代，您将加载一批 100 个示例，这些示例将被馈送到 session 中:
y_ = tf.placeholder(tf.float32,[None,10])
batch_x,batch_y = mnist.train.next_batch(100)
sess.run(train_step,feed_dict={x:batch_x,y_:batch_y})
我猜你的困惑是因为在 session.run() 期间必须将 batch_x 分配给 x，而 batch_y 被输入 y_。这样做的原因是训练图像 (x) 来自 MNIST 数据集，正确的标签 (y_) 也是如此，而您的模型输出/预测 ( y) 由您的卷积神经网络计算。
您将一批输入图像提供给您的 session 。您的模型对它认为该图像属于哪个类别的每个图像进行预测，最后将这些预测与正确的标签进行比较。这些步骤的最后一步在您的代码的以下行中执行:
cross_entropy = tf.nn.softmax_cross_entropy_with_logits(labels=y_,logits=y)
如您所见，通过向交叉熵函数传递来自您的数据集和预测的正确标签来调用交叉熵函数，这些标签由您的模型“即时”计算。这就是为什么必须在 session 运行期间向 y_ 传递数据，而不必对 y 执行相同的操作。
