'The tensorflow global_step, i.e. how many times ``hooked_sess.run`` has been called.
Note:
1. global_step is incremented **after** each ``hooked_sess.run`` returns from TF runtime.
2. If you make zero or more than one calls to ``hooked_sess.run`` in one
:meth:`run_step`, local_step and global_step may increment at different speed.'

@property
def global_step(self):

    return self._global_step
