formatter created with logging.Formatter caused ValueError and RecursionError

[Karmenzind]

My setup code:

    loki_handler = LokiLoggerHandler(
        url=LOKI_ADDR + "/loki/api/v1/push",
        labels={"service_name": PROJECT_NAME},
        label_keys={"level": "level"},
        timeout=10,
        enable_self_errors=True,
    )
    loki_handler.setFormatter(logging.Formatter(plain_fmt))

According to the README, logging.Formatter is supposed to be supportted, but it actually isn't. Here's the error I encountered:

Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/loki_logger_handler/loki_logger_handler.py", line 103, in emit
    formatted_record, log_loki_metadata = self.formatter.format(record)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: too many values to unpack (expected 2)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/loki_logger_handler/loki_logger_handler.py", line 103, in emit
    formatted_record, log_loki_metadata = self.formatter.format(record)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: too many values to unpack (expected 2)

During handling of the above exception, another exception occurred:

(...and many duplicated logs...)

Seems that the recursive errors are due to enable_self_errors=True

In the source code of logging, logging.Formatter only returns 1 value:

[xente]

You can use your own custom format but it must return two values, just like logger_formatter.py and loguru_formatter.py.

If you can point me to where the documentation says logging.Formatter is supported, I’ll update this to avoid any confusion.

[Karmenzind]

Thanks for your reply.

I assumed the logging.Formatter here means a type hint. Please check.

[TomW1605]

Hi, i just ran into this and was also confused because the docs say it should be supported. can i sugest that rather than update the docs it would be far better to update the code to support using a standard logging formatter. from looking at the error and the code i think the only thing that is really needed is to not unpack direct result of the format call and simply check if it is 1 or 2 items. if it is only 1 then use a default empty dict for the log_loki_metadata value. that way standard formatter objects work at the cost of not supporting setting the loki metadata in the log call and if people want to write their own custom formatter to handle that they can

EDIT: ok, having taken a closer look its not quite that simple. however i think that is because the "formatter" that is bundled with this library is not actually a formatter. it is really more of a parser or converter, taking the log record and extracting the data the library needs. if this was renamed and not used as a formatter with then a standard formatter allowed to be used for the message format itself and the existing one used to generate the loki metadata like it is doing now i think that would be a good solution

EDIT 2: done a bit more going through things and while i think this can be made to work better i think it would need a significant change to how the data is processed and passed through the functions.

i do still think calling the function you have a "formatter" in the context of something working with the logging library is a bit confusing since it dosnt work at all like the stock ones