def GetTZInfo(tzname='UTC', utcOffset=None, dst=None):
      """ Get / Add timezone info """
      key = (tzname, utcOffset, dst)
      tzInfo = TZManager._tzInfos.get(key)
      if not tzInfo:
         tzInfo = TZInfo(tzname, utcOffset, dst)
         TZManager._tzInfos[key] = tzInfo
      return tzInfo
Get / Add timezone info