[HELP] Logging Basic Python Class Only

[TWDickson]

I've got a basic python class that and an interpreter written that translates my class into JSON

class LogMessage:
    def __init__(self, message):
        self.timestamp = datetime.datetime.now()
        self.message = message

    def __str__(self):
        return f"{self.timestamp.isoformat()}: {self.message}"

class LogMessageEncoder(JSONEncoder):
    """
    JSON Encoder for Name Match Diagnostic Class
    """

    def default(self, o):
        # Rough conversion
        temp = o.__dict__
        for e in temp.keys():
            if isinstance(temp[e], datetime.datetime):
                temp[e] = temp[e].isoformat()
        return temp

logger = logging.getLogger()
logHandler = logging.FileHandler(f"logs/{datetime.datetime.today().strftime('%Y-%m-%dT%H-%M-%S')}-JSON-Log.log")
formatter = jsonlogger.JsonFormatter(json_encoder=modules.log_message.LogMessageEncoder)
logHandler.setFormatter(formatter)
logger.addHandler(logHandler)
logger.setLevel(logging.DEBUG)

logger.debug(LogMessage("foo"))

# logs as {"message": "2020-11-13T14:45:56.602299: foo"}

How would I log just the class (and subclasses)? without something like "message" it seems that the logger is using the str representation instead of the encoder.