Don't allow passing in loguru

[crizCraig]

Loguru is not api compatible with standard logging despite efforts in #294, so it may be best to raise an error or wrap the loguru logger with a standard logger when doing this

from loguru import logger
@retry(
    stop=stop_after_attempt(10),
    wait=wait_random_exponential(multiplier=1, max=10),
    reraise=True,
    before_sleep=before_sleep_log(logger, "ERROR"),  # type: ignore
    after=after_log(logger, "ERROR"),  # type: ignore
)

As it can cause a KeyError due to this

Here's a wrapping approach which may be the best thing for people to setup in accordance with their own logging needs. Not sure if @Delgan has a better approach though.

[Delgan]

Hi there.

As per the type-hints in the source code of tenacity, the logger parameter is clearly expecting a standard logging.Logger object:

tenacity/tenacity/before_sleep.py

Lines 31 to 36 in 3100582

	def before_sleep_log(
	logger: "logging.Logger",
	log_level: int,
	exc_info: bool = False,
	) -> typing.Callable[["RetryCallState"], None]:
	"""Before call strategy that logs to some logger the attempt."""

Consequently, users should not expect tenacity to be compatible with Loguru's logger, nor should tenacity developers necessarily care about that. The compatibility error should be raised by static linters such as Mypy.

In this situation, the most appropriate workaround is for users to define a standard logger wrapping Loguru's logger to bridge the gap between the two libraries. I added more details in Delgan/loguru#1008 (comment).