python logging module problem

[Peter Otten]

Ritesh Raj Sarraf wrote:

> Vinay Sajip wrote:

>> It's usual to rely on logger levels and to set handler levels for
>> additional refinement of what goes to a particular handler's
>> destination.
 
> The problem is that for StreamHandler, logging module logs to
> sys.stderr.
> I want to use the logging feature for most of the messages my program
> displays.
> 
> So some messages would be going to sys.stdout and some to sys.stderr.
> 
> So, I'm ended up creating two handlers, one for sys.stdout and the
> other for sys.stderr.
> I'd then make INFO level messages go to sys.stdout and DEBUG level
> messages go to sys.stderr.
> 
> What do you suggest ??
> Is it good doing this way ?

You can achieve the desired behaviour by adding a custom Filter:

import sys
import logging

logger = logging.getLogger("my_app")
logger.setLevel(logging.DEBUG)

class LevelFilter(logging.Filter):
    def __init__(self, level):
        self.level = level
    def filter(self, record):
        return self.level == record.levelno

def make_handler(outstream, format, level):
    handler = logging.StreamHandler(outstream)
    formatter = logging.Formatter(format)
    handler.setFormatter(formatter)
    handler.addFilter(LevelFilter(level))
    return handler

logger.addHandler(make_handler(sys.stderr,
    'STDERR %(levelname)s %(message)s', logging.WARN))
logger.addHandler(make_handler(sys.stdout,
    'STDOUT %(levelname)s %(message)s', logging.INFO))

logger.info("the world is flat")
logger.warning("take care not to fall off its rim")

Not sure whether this is a good idea. Another way might be to use distinct
loggers.

Peter