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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _resolve_sort_by(sort_by, flag_radius_query):
 """ Result ``sort_by`` argument. :param sort_by: str, or sqlalchemy ORM attribute. :param flag_radius_query: :return: """

        if sort_by is None:
            if flag_radius_query:
                sort_by = SORT_BY_DIST
        elif isinstance(sort_by, string_types):
            if sort_by.lower() == SORT_BY_DIST:
                if flag_radius_query is False:
                    msg = "`sort_by` arg can be 'dist' only under distance based query!"
                    raise ValueError(msg)
                sort_by = SORT_BY_DIST
            elif sort_by not in SimpleZipcode.__table__.columns:
                msg = "`sort_by` arg has to be one of the Zipcode attribute or 'dist'!"
                raise ValueError(msg)
        else:
            sort_by = sort_by.name

        return sort_by