title: TensorFlow's Print is not printing
body: <p>I am trying to understand some code from a reinforcement learning algorithm. In order to do that I am trying to print the value of a tensor.</p>
  
  <p>I made a simple piece of code to show what I mean.</p>
  
  <pre><code>import tensorflow as tf
  from keras import backend as K
  
  x = K.abs(-2.0)
  tf.Print(x,[x], 'x')
  </code></pre>
  
  <p>The goal is to have the value '2' printed(the absolute value of -2). But I only get back the following:</p>
  
  <pre><code>Using TensorFlow backend.
  
  Process finished with exit code 0
  </code></pre>
  
  <p>Nothing, how can I print the value '2' just like a print('...') statement would do?</p>