Can Python's logging format be modified depending on the message log level?

Question

I'm using Python's logging mechanism to print output to the screen. I could do this with print statements, but I want to allow a finer-tuned granularity for the user to disable certain types of output. I like the format printed for errors, but would prefer a simpler format when the output level is "info."

For example:

  logger.error("Running cmd failed")
  logger.info("Running cmd passed")

In this example, I would like the format of the error to be printed differently:

# error
Aug 27, 2009 - ERROR: Running cmd failed
# info
Running cmd passed

Is it possible to have different formats for different log levels without having multiple logging objects? I'd prefer to do this without modifying the logger once it's created since there are a high number of if/else statements to determine how the output should be logged.

Answer 1

I just ran into this issue and had trouble filling in the "holes" left in the above example. Here's a more complete, working version that I used. Hopefully this helps someone:

# Custom formatter
class MyFormatter(logging.Formatter):

    err_fmt  = "ERROR: %(msg)s"
    dbg_fmt  = "DBG: %(module)s: %(lineno)d: %(msg)s"
    info_fmt = "%(msg)s"


    def __init__(self, fmt="%(levelno)s: %(msg)s"):
        logging.Formatter.__init__(self, fmt)


    def format(self, record):

        # Save the original format configured by the user
        # when the logger formatter was instantiated
        format_orig = self._fmt

        # Replace the original format with one customized by logging level
        if record.levelno == logging.DEBUG:
            self._fmt = MyFormatter.dbg_fmt

        elif record.levelno == logging.INFO:
            self._fmt = MyFormatter.info_fmt

        elif record.levelno == logging.ERROR:
            self._fmt = MyFormatter.err_fmt

        # Call the original formatter class to do the grunt work
        result = logging.Formatter.format(self, record)

        # Restore the original format configured by the user
        self._fmt = format_orig

        return result

Edit:

Compliments of Halloleo, here's an example of how to use the above in your script:

fmt = MyFormatter()
hdlr = logging.StreamHandler(sys.stdout)

hdlr.setFormatter(fmt)
logging.root.addHandler(hdlr)
logging.root.setLevel(DEBUG)

Edit 2:

Python3 logging has changed a bit. See here for a Python3 approach.