title: Tensorflow how to get tensor value
body: <p>In python I can use</p>
  
  <pre><code>a = np.array([[3], [6], [9]])
  </code></pre>
  
  <p>Obviously,</p>
  
  <pre><code>a[0][0] = 3
  a[1][0] = 6
  a[2][0] = 9
  </code></pre>
  
  <p>But I tried to do the same thing with tensorflow</p>
  
  <pre><code>import tensorflow as tf
  a = tf.Variable(np.array([[3], [6], [9]]))
  init = tf.initialize_all_variables()
  
  with tf.Session() as ss:
     ss.run(init)
     for i in range(3):
         print sess.run(a[i][0])
  </code></pre>
  
  <p>If I print it(use for loop), I got <code>TypeError: 'Variable' object is not callable</code></p>
  
  <p>How can I resolve this error?
  Thanks very much for any help!</p>