def find_action_name_by_value(registry, target_action_instance):
    """the association of a name of an action class with a human readable
    string is exposed externally only at the time of argument definitions.
    This routine, when given a reference to argparse's internal action
    registry and an action, will find that action and return the name under
    which it was registered.
    """
    target_type = type(target_action_instance)
    for key, value in six.iteritems(registry['action']):
        if value is target_type:
            if key is None:
                return 'store'
            return key
    return None