Thursday 24 September 2009

How to treat a logger like an output stream

Sometimes, you need to interface to a third-party API which expects a file-like object to write to, but you want to direct the API's output to a logger. You can do this using a LoggerWriter, which wraps a logger with a file-like API. Here's a short script illustrating the class:

import logging

class LoggerWriter:
    def __init__(self, logger, level):
        self.logger = logger
        self.level = level

    def write(self, message):
        if message != '\n':
            self.logger.log(self.level, message)

def main():
    logger = logging.getLogger("demo")
    info_fp = LoggerWriter(logger, logging.INFO)
    debug_fp = LoggerWriter(logger, logging.DEBUG)
    print >> info_fp, "An INFO message"
    print >> debug_fp, "A DEBUG message"

if __name__ == "__main__":

When run, the script prints:

INFO:demo:An INFO message
DEBUG:demo:An DEBUG message

Many thanks to Barry Warsaw for the suggestion.

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