Logging in Python with Tornado's pretty print formatter and routing all messages with INFO level and above to STDOUT, and all messages below to STDERR.

custom_logging.py

#!/usr/bin/env python
import sys
import logging
import tornado.log

# For pretty log messages, if available
try:
    import curses
except ImportError:
    curses = None

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)

def setup_custom_logging():
    color = False
    if curses and sys.stderr.isatty():
        try:
            curses.setupterm()
            if curses.tigetnum("colors") > 0:
                color = True
        except Exception:
            pass
    h1 = logging.StreamHandler(sys.stdout)
    h1.setFormatter(tornado.log.LogFormatter(color=color))
    f1 = _SingleLevelFilter(logging.INFO, False)
    h1.addFilter(f1)
    rootLogger = logging.getLogger()
    rootLogger.addHandler(h1)
    h2 = logging.StreamHandler(sys.stderr)
    h2.setFormatter(tornado.log.LogFormatter(color=color))
    f2 = _SingleLevelFilter(logging.INFO, True)
    h2.addFilter(f2)
    rootLogger.addHandler(h2)