Parse a non-day fixed value

def _parse_req(requnit, reqval):
        ''' Parse a non-day fixed value '''
        assert reqval[0] != '='

        try:
            retn = []
            for val in reqval.split(','):
                if requnit == 'month':
                    if reqval[0].isdigit():
                        retn.append(int(reqval))  # must be a month (1-12)
                    else:
                        try:
                            retn.append(list(calendar.month_abbr).index(val.title()))
                        except ValueError:
                            retn.append(list(calendar.month_name).index(val.title()))
                else:
                    retn.append(int(val))
        except ValueError:
            return None

        if not retn:
            return None

        return retn[0] if len(retn) == 1 else retn