Documented worse than I’d like to.

Filters allow to do things to the records (structs that make up a log message later), be it change them in place or don’t let them pass.

You can pass a function in place of a Filter, it should:

• get a logging.LogRecord
• optionally change it in place
• decide whether to let it pass
• return 0 for no, non-zero for yes

The fields of a LogRecord are the same ones we name when doing formatting: name, lineno, msg and friends.

If your Filter tries to log something in a way that it’ll get filtered through it, you get recursion.

Sample of a filter that removes specific matches and gets added to a Handler:

def filter(record: logging.LogRecord) -> int:
	"""Filters away log records containing annoying stuff."""
	blacklist_condition = (
		(
			record.name == "lib_sdk.data"
			and "not available on your" in record.msg
		)
		or (
			record.name == "lib_sdk.data"
			and record.levelno == logging.WARNING
			and "which is legacy" in record.msg
		)
		or (
			record.name == "lib_sdk.data"
			and record.levelno == logging.WARNING
			and "created but without information" in record.msg
		)
	)
	if blacklist_condition:
		return 0
	else:
		return 1

sh = logging.StreamHandler()
sh.addFilter(filter)

Much better than what I had before (220914-2249 Python logging change level through context manager and operator magic).

One can go crazy here with regexes etc. but I shan’t.