def getTzid(tzid, smart=True):
    """Return the tzid if it exists, or None."""
    tz = __tzidMap.get(toUnicode(tzid), None)
    if smart and tzid and not tz:
        try:
            from pytz import timezone, UnknownTimeZoneError
            try:
                tz = timezone(tzid)
                registerTzid(toUnicode(tzid), tz)
            except UnknownTimeZoneError:
                pass
        except ImportError:
            pass
    return tz
Return the tzid if it exists, or None.