How to specify levels in python logging module?

Question

I need two handlers. One for file logging and another one for stream logging in the console. I need to specify levels for each handler. Notice that my levels are going to be something like the following ones.

Stream Handler –> INFO

File Handler –> WARNING, ERROR, CRITICAL

Here is my code.

    # Create a custom logger
    logger = logging.getLogger('DBMQ')
    logger.setLevel(logging.DEBUG)

    stream_handler = logging.StreamHandler()
    stream_handler.setLevel(logging.INFO)

    logger.addHandler(stream_handler)

    file_handler = logging.FileHandler('./data/file.log')
    file_handler.setLevel(logging.WARNING)

    logger.addHandler(file_handler)

Now, it has to operate like this:

logger.debug('hey') # Nothing should happen
logger.info('hey') # only stream handler should log this message
logger.warning('hey') # only file handler should log this message but the stream does too
logger.error('hey') # only file handler should log this message but the stream does too
logger.critical('hey') # only file handler should log this message but the stream does too

I need to disallow the stream handler from logging the warning, error, and critical logging levels. Is there any way to filter this handler?

Asked By: Sadra

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Source

Answer 1

You could create your own Handler:

logger = logging.getLogger('DBMQ')
logger.setLevel(logging.DEBUG)


class MyStreamHandler(logging.StreamHandler):
    def emit(self, record):
        if record.levelno == self.level:
            super().emit(record)

stream_handler = MyStreamHandler()
stream_handler.setLevel(logging.INFO)

logger.addHandler(stream_handler)

file_handler = logging.FileHandler('./data/file.log')
file_handler.setLevel(logging.WARNING)

logger.addHandler(file_handler)

Answered By: Lufftre

Answer 2

The "level" system does not work to as disable/enable single "levels".
https://docs.python.org/3/library/logging.html#logging-levels

The "level" is a single integer value. If the message’s level is over logger/handler level, it will be showed. Just that simple.

If you need another logic the only way is implement you own handlers.

Answered By: pbacterio

Answer 3

I liked Lufftre’s answer here, but I don’t like the idea of creating a whole class just for this, so I’m basically patching the StreamHandler’s emit function into a lambda function, like so:

chs = logging.StreamHandler()
chs.setLevel(logging.INFO)
chs.semit = chs.emit # You have to "clone" original emit, as there is no super()
chs.emit = lambda record: chs.semit(record) if record.levelno == chs.level else None
logger.addHandler(chs)

I think it looks cleaner. If you want multiple handlers working in this way, then you can first define a function that is this lambda and then patch the emit with that function object.

# Set up new emit
nemit = lambda record, sh: sh.semit(record) if record.levelno == sh.level else None

# Create first handler
ch = logging.StreamHandler()
ch.setLevel(logging.ERROR)
ch.semit = ch.emit 
ch.emit = lambda record: nemit(record, ch)

# Create second handler
chs = logging.StreamHandler()
chs.setLevel(logging.INFO)
chs.semit = chs.emit
chs.emit = lambda record: nemit(record, chs)

logger.addHandler(ch)
logger.addHandler(chs)

Answered By: Crad

How to specify levels in python logging module?

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