Logging Cookbook shows incorrect logger configurations

[giodueck]

Documentation

Several examples in the Logging Cookbook page show that setting a log level per handler via logging.config.dictConfig() is supposed to limit that handler to that level and above, just like the root logger has a level:

• https://docs.python.org/3/howto/logging-cookbook.html#custom-handling-of-levels
• https://docs.python.org/3/howto/logging-cookbook.html#logging-to-a-single-file-from-multiple-processes

AFAICT handlers don't actually allow filtering levels by setting a "level" field (tested with 3.12.9), and it must instead be done through a filter (similar to the one used in the first example).

The correct snippet for the first example would be something akin to the following:

LOGGER_CONFIG = '''
{
    "version": 1,
    "disable_existing_loggers": false,
    "filters": {
        "warnings_and_below": {
            "()" : "__main__.filter_below",
            "level": "WARNING"
        },
        "errors_and_above": {
            "()" : "__main__.filter_above",
            "level": "ERROR"
        }
    },
    "handlers": {
        "stdout": {
            "class": "logging.StreamHandler",
            "filters": ["warnings_and_below"],
            "stream": "ext://sys.stdout"
        },
        "stderr": {
            "class": "logging.StreamHandler",
            "filters": ["errors_and_above"],
            "stream": "ext://sys.stderr"
        }
    },
    "root": {
        "level": "DEBUG",
        "handlers": [
            "stdout",
            "stderr"
        ]
    }
}
'''

def filter_below(level):
    level = getattr(logging, level)

    def filter(record):
        return record.levelno <= level

    return filter

def filter_above(level):
    level = getattr(logging, level)

    def filter(record):
        return record.levelno >= level

    return filter

It took a while to figure that out as a beginner, but looking at logging.handlers made me doubt these examples.