Logging, StreamHandler and standard streams

Question

I can't figure out how to log info-level messages to stdout, but everything else to stderr. I already read this http://docs.python.org/library/logging.html. Any suggestion?

Answer 1

The following script, log1.py:

import logging, sys  class SingleLevelFilter(logging.Filter):     def __init__(self, passlevel, reject):         self.passlevel = passlevel         self.reject = reject      def filter(self, record):         if self.reject:             return (record.levelno != self.passlevel)         else:             return (record.levelno == self.passlevel)  h1 = logging.StreamHandler(sys.stdout) f1 = SingleLevelFilter(logging.INFO, False) h1.addFilter(f1) rootLogger = logging.getLogger() rootLogger.addHandler(h1) h2 = logging.StreamHandler(sys.stderr) f2 = SingleLevelFilter(logging.INFO, True) h2.addFilter(f2) rootLogger.addHandler(h2) logger = logging.getLogger("my.logger") logger.setLevel(logging.DEBUG) logger.debug("A DEBUG message") logger.info("An INFO message") logger.warning("A WARNING message") logger.error("An ERROR message") logger.critical("A CRITICAL message") 

when run, produces the following results.

 C:\temp>log1.py A DEBUG message An INFO message A WARNING message An ERROR message A CRITICAL message 

As you'd expect, since on a terminal sys.stdout and sys.stderr are the same. Now, let's redirect stdout to a file, tmp:

 C:\temp>log1.py >tmp A DEBUG message A WARNING message An ERROR message A CRITICAL message 

So the INFO message has not been printed to the terminal - but the messages directed to sys.stderr have been printed. Let's look at what's in tmp:

 C:\temp>type tmp An INFO message 

So that approach appears to do what you want.