def parse_datetime(datetimestring):
    '''
    Parses ISO 8601 date-times into datetime.datetime objects.
    This function uses parse_date and parse_time to do the job, so it allows
    more combinations of date and time representations, than the actual
    ISO 8601:2004 standard allows.
    '''
    try:
        datestring, timestring = re.split('T| ', datetimestring)
    except ValueError:
        raise isodate.ISO8601Error(
            "ISO 8601 time designator 'T' or ' '  missing. Unable to parse "
            "datetime string %r" % datetimestring
        )
    tmpdate = isodate.parse_date(datestring)
    tmptime = isodate.parse_time(timestring)
    return datetime.datetime.combine(tmpdate, tmptime)