@staticmethod
def _idxr_for_frame(idxr):
    """
        Change idxr to make sure indexing a DataFrame will return a DataFrame
        and indexing a Series will return a Series.
        :param idxr: (indexes, columns)
        :type idxr: tuple
        :return: tuple
        """
    if isinstance(idxr[0], (str, int, float)):
        idxr = [idxr[0]], idxr[1]
    if isinstance(idxr[1], (str, int, float)):
        idxr = idxr[0], [idxr[1]]
    return idxr
