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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def format(self, record: logging.LogRecord) -> str: """ Formats a record and serializes it as a JSON str. If record message isnt already a dict, initializes a new dict and uses `default_msg_fieldname` as a key as the record msg as the value. """

        msg: Union[str, dict] = record.msg
        if not isinstance(record.msg, dict):
            msg = {self.default_msg_fieldname: msg}

        if record.exc_info:  # type: ignore
            msg["exc_info"] = record.exc_info
        if record.exc_text:  # type: ignore
            msg["exc_text"] = record.exc_text  # type: ignore

        return self.serializer(msg, default=self._default_handler)