code: def GetMessage(self, log_source, lcid, message_identifier):
      
      event_log_provider_key = self._GetEventLogProviderKey(log_source)
      if not event_log_provider_key:
        return None
  
      generator = self._GetMessageFileKeys(event_log_provider_key)
      if not generator:
        return None
  
      # TODO: cache a number of message strings.
      message_string = None
      for message_file_key in generator:
        message_string = self._GetMessage(
            message_file_key, lcid, message_identifier)
  
        if message_string:
          break
  
      if self._string_format == 'wrc':
        message_string = self._ReformatMessageString(message_string)
  
      return message_string
docs: Retrieves a specific message for a specific Event Log source.
  
      Args:
        log_source (str): Event Log source.
        lcid (int): language code identifier (LCID).
        message_identifier (int): message identifier.
  
      Returns:
        str: message string or None if not available.