'Return element returned by \'get_or_add_\' method for *prop_name*.'

def _get_or_add(self, prop_name):

    get_or_add_method_name = (u'get_or_add_%s' % prop_name)
    get_or_add_method = getattr(self, get_or_add_method_name)
    element = get_or_add_method()
    return element
