title: Display python variable in tensorboard
body: <p>i wanna display some python variables in tensorboard, but i dont get it done.</p>
  
  <p>My code so far, display only a line in tensorboard for the lines with static number, if i use the outcommented-lines, it does not work ? It then prints:
  ValueError: Shapes () and (?,) are not compatible</p>
  
  <p>Someone has an idea?</p>
  
  <pre><code>import tensorflow as tf
  
  step = 0
  session = tf.Session()
  
  tensorboardVar = tf.Variable(0, "tensorboardVar")
  
  pythonVar = tf.placeholder("int32", [None])
  
  #update_tensorboardVar = tensorboardVar.assign(pythonVar)
  update_tensorboardVar = tensorboardVar.assign(4)
  tf.scalar_summary("myVar", update_tensorboardVar)
  
  merged = tf.merge_all_summaries()
  
  sum_writer = tf.train.SummaryWriter('/tmp/train/c/', session.graph)
  
  session.run(tf.initialize_all_variables())
  
  
  for i in range(100):
          _, result = session.run([update_tensorboardVar, merged])
          #_, result = session.run([update_tensorboardVar, merged], feed_dict={pythonVar: i})
          sum_writer.add_summary(result, step)
          step += 1
  </code></pre>