title: How to get epoch num info from tf.train.string_input_producer
body: <p>If reading files using string_input_producer, like</p>
  
  <pre><code>filename_queue = tf.train.string_input_producer(
    files, 
    num_epochs=num_epochs,
    shuffle=shuffle)
  </code></pre>
  
  <p>how can I get epoch num info during training(I want to show this info during training)
  I tried below</p>
  
  <pre><code>run 
  tf.get_default_graph().get_tensor_by_name('input_train/input_producer/limit_epochs/epochs:0')
  </code></pre>
  
  <p>will always the same as the limit epoch num.</p>
  
  <pre><code>run
  tf.get_default_graph().get_tensor_by_name('input_train/input_producer/limit_epochs/CountUpTo:0')
  </code></pre>
  
  <p>will each time add 1..</p>
  
  <p>Both can not get correct epoch num during training.</p>
  
  <p>Another thing is ,if retrain from existing model, can I got the epoch num info already trained?</p>