Quick start logging. Here are some short examples of logging in Python 2.7.

Basic logging to file

import logging
# change default log entry format, set filename and logging level
logging.basicConfig(level=logging.INFO, format="%(asctime)s %(levelname)s %(message)s", filename="example.log")
logging.info("Started")
logging.info("This is an example entry")
logging.debug("This line won't get logged as the log level is INFO")
logging.info("Done.")
# perform an orderly shutdown by flushing and closing all handlers; called at application exit and no further use of the logging system should be made after this call.
logging.shutdown()

Slightly less basic

Logging to file and console

import logging
import logging.handlers

# log file name and logging message level
log_file_name = 'loggingexample.log'
log_level = logging.INFO

# log record format string
format_string = '%(asctime)s %(name)s %(levelname)s %(message)s'

# set default logging (to console)
logging.basicConfig(level=log_level, format=format_string)

# set logging to file
log_formatter = logging.Formatter(format_string)
file_handler = logging.FileHandler(log_file_name, mode='w') # mode is file write mode, 'a' to append
file_handler.setFormatter(log_formatter)

# create child logger and set it to be a file handler
logger = logging.getLogger() # or pass a string to give it a name
logger.addHandler(file_handler)
logger.setLevel(log_level)

# log some messages
logger.info("Started")
logger.info("This is an example entry")
logger.debug("This line won't get logged as the log level is INFO")
logger.info("Done.")

# perform an orderly shutdown by flushing and closing all handlers; called at application exit and no further use of the logging system should be made after this call.
logging.shutdown()

TimedRotatingFileHandler

Official docs: http://docs.python.org/library/logging.handlers.html#timedrotatingfilehandler

This log handler is really useful for regularly scheduled scripts as the logs get rotated rather than filing all available space given enough time.

#!/usr/bin/env python
#-------------------------------------------------------------------------------
# Name: example-TimedRotatingFileHandler.py
# Purpose: Write log using TimedRotatingFileHandler
# Author: Adrian Jones
# Created: 2012-05-25
#
# TimedRotatingFileHandler: from handler.py source:
# Current 'when' events supported:
#   S - Seconds
#   M - Minutes
#   H - Hours
#   D - Days
#   midnight - roll over at midnight
#   W{0-6} - roll over on a certain day; 0 - Monday
#
# Case of the 'when' specifier is not important; lower or upper case
# will work.
#
# Interval is in seconds
# backupCount in number of old log files to keep
#
#-------------------------------------------------------------------------------
import time
import logging
import logging.handlers
log_file_name = 'TimedRotatingFileHandler.log'
logging_level = logging.DEBUG
try:
    # set TimedRotatingFileHandler for root
    formatter = logging.Formatter('%(asctime)s %(name)s %(levelname)s %(message)s')
    # use very short interval for this example, typical 'when' would be 'midnight' and no explicit interval
    handler = logging.handlers.TimedRotatingFileHandler(log_file_name, when="S", interval=30, backupCount=10)
    handler.setFormatter(formatter)
    logger = logging.getLogger() # or pass string to give it a name
    logger.addHandler(handler)
    logger.setLevel(logging_level)
    # generate lots of example messages
    for i in range(10000):
        time.sleep(0.1)
        logger.debug('i=%d' % i)
        logger.info('i=%d' % i)
        logger.warn('i=%d' % i)
        logger.error('i=%d' % i)
        logger.critical('i=%d' % i)
except KeyboardInterrupt:
    # handle Ctrl-C
    logging.warn("Cancelled by user")
except Exception as ex:
    # handle unexpected script errors
    logging.exception("Unhandled error\n{}".format(ex))
    raise
finally:
    # perform an orderly shutdown by flushing and closing all handlers; called at application exit and no further use of the logging system should be made after this call.
    logging.shutdown()