title: What does TensorFlow shape (?,) mean?
body: <p>I'm getting the shape of a TensofFlow tensor as:</p>
  
  <p><code>(?,)</code></p>
  
  <p><a href="https://stackoverflow.com/a/40953146/5353461">This answer</a> says that the <code>?</code> means that the dimension is not fixed in the graph and it can vary between run calls.</p>
  
  <p>What does the <code>?</code> mean in conjuction with the trailing comma?</p>
  
  <p>Documentation chapter and verse would be appreciated. I find syntax very difficult to google.</p>