code: def getTzid(tzid, smart=True):
      
      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
docs: Return the tzid if it exists, or None.