title: Tensorflow: feed dict error: You must feed a value for placeholder tensor
body: <p>I have one bug I cannot find out the reason. Here is the code:</p>
  
  <pre><code>with tf.Graph().as_default():
          global_step = tf.Variable(0, trainable=False)
  
          images = tf.placeholder(tf.float32, shape = [FLAGS.batch_size,33,33,1])
          labels = tf.placeholder(tf.float32, shape = [FLAGS.batch_size,21,21,1])
  
          logits = inference(images)
          losses = loss(logits, labels)
          train_op = train(losses, global_step)
          saver = tf.train.Saver(tf.all_variables())
          summary_op = tf.merge_all_summaries()
          init = tf.initialize_all_variables()
  
          sess = tf.Session()
          sess.run(init)                                                 
  
          summary_writer = tf.train.SummaryWriter(FLAGS.train_dir, sess.graph)
  
          for step in xrange(FLAGS.max_steps):
              start_time = time.time()
  
              data_batch, label_batch = SRCNN_inputs.next_batch(np_data, np_label,
                                                                FLAGS.batch_size)
  
  
              _, loss_value = sess.run([train_op, losses], feed_dict={images: data_batch, labels: label_batch})
  
              duration = time.time() - start_time
  
  def next_batch(np_data, np_label, batchsize, 
                 training_number = NUM_EXAMPLES_PER_EPOCH_TRAIN):
  
      perm = np.arange(training_number)
      np.random.shuffle(perm)
      data = np_data[perm]
      label = np_label[perm]
      data_batch = data[0:batchsize,:]
      label_batch = label[0:batchsize,:]
  
  
  return data_batch, label_batch
  </code></pre>
  
  <p>where <code>np_data</code> is the whole training samples read from hdf5 file, and the same to <code>np_label</code>.</p>
  
  <p>After I run the code, I got the error like this :</p>
  
  <pre><code>2016-07-07 11:16:36.900831: step 0, loss = 55.22 (218.9 examples/sec; 0.585 sec/batch)
  Traceback (most recent call last):
  
    File "&lt;ipython-input-1-19672e1f8f12&gt;", line 1, in &lt;module&gt;
      runfile('/home/kang/Documents/work_code_PC1/tf_SRCNN/SRCNN_train.py', wdir='/home/kang/Documents/work_code_PC1/tf_SRCNN')
  
    File "/usr/lib/python3/dist-packages/spyderlib/widgets/externalshell/sitecustomize.py", line 685, in runfile
      execfile(filename, namespace)
  
    File "/usr/lib/python3/dist-packages/spyderlib/widgets/externalshell/sitecustomize.py", line 85, in execfile
      exec(compile(open(filename, 'rb').read(), filename, 'exec'), namespace)
  
    File "/home/kang/Documents/work_code_PC1/tf_SRCNN/SRCNN_train.py", line 155, in &lt;module&gt;
      train_test()
  
    File "/home/kang/Documents/work_code_PC1/tf_SRCNN/SRCNN_train.py", line 146, in train_test
      summary_str = sess.run(summary_op)
  
    File "/usr/local/lib/python3.4/dist-packages/tensorflow/python/client/session.py", line 372, in run
      run_metadata_ptr)
  
    File "/usr/local/lib/python3.4/dist-packages/tensorflow/python/client/session.py", line 636, in _run
      feed_dict_string, options, run_metadata)
  
    File "/usr/local/lib/python3.4/dist-packages/tensorflow/python/client/session.py", line 708, in _do_run
      target_list, options, run_metadata)
  
    File "/usr/local/lib/python3.4/dist-packages/tensorflow/python/client/session.py", line 728, in _do_call
      raise type(e)(node_def, op, message)
  
  InvalidArgumentError: You must feed a value for placeholder tensor 'Placeholder' with dtype float and shape [128,33,33,1]
       [[Node: Placeholder = Placeholder[dtype=DT_FLOAT, shape=[128,33,33,1], _device="/job:localhost/replica:0/task:0/gpu:0"]()]]
       [[Node: truediv/_74 = _Recv[client_terminated=false, recv_device="/job:localhost/replica:0/task:0/cpu:0", send_device="/job:localhost/replica:0/task:0/gpu:0", send_device_incarnation=1, tensor_name="edge_56_truediv", tensor_type=DT_FLOAT, _device="/job:localhost/replica:0/task:0/cpu:0"]()]]
  Caused by op 'Placeholder', defined at:
  </code></pre>
  
  <p>So, It shows that for the step 0 it has the result, which means that the data has been fed into the Placeholders. </p>
  
  <p>But why does it come the error of feeding data into Placeholder in the next time?</p>
  
  <p>When I try to comment the code <code>summary_op = tf.merge_all_summaries()</code> and the code works fine. why is it the case?</p>