title: Retrieve global step number from tf.train.summary_iterator
body: <p>I am using <code>tf.train.summary_iterator</code> to read data stored in an event file. I would like to access the global step number at which a particular summary was stored, but the <a href="https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/summary.proto" rel="nofollow noreferrer"><code>summary.proto</code></a> has no reference to step number. Tensorboard seems to have access to this information, so I think there might be a way to do this, but I have not been able to track it down.</p>