Returns:
        tf.Tensor: the global_step variable in the current graph. Create if doesn't exist.

def get_global_step_var():
    """
    Returns:
        tf.Tensor: the global_step variable in the current graph. Create if doesn't exist.
    """
    scope = tfv1.VariableScope(reuse=False, name='')  # the root vs
    with tfv1.variable_scope(scope):
        var = tfv1.train.get_or_create_global_step()
    return var