Python logging example

logging_demo.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

# Python logging demo from https://gist.github.com/miebach/5349852

import logging

# see http://www.shutupandship.com/2012/02/how-python-logging-module-works.html

def init_file_logger(fname="log.txt",threshhold_level="info",logger_instance=""):
  # Initialize a new logger instance and optionally return it.
  # You can later always get the instance by calling logging.getLogger(logger_instance)
  # Levels are CRITICAL <- ERROR <- WARNING <- INFO <- DEBUG
  h = logging.FileHandler(fname)
  l = logging.getLogger(logger_instance)
  l.handlers=[]
  l.addHandler(h)
  if threshhold_level == "debug":
    l.setLevel(logging.DEBUG)
  elif threshhold_level == "info":
    l.setLevel(logging.INFO)
  elif threshhold_level == "warning":
    l.setLevel(logging.WARNING)
  elif threshhold_level == "error":
    l.setLevel(logging.ERROR)
  elif threshhold_level == "critical":
    l.setLevel(logging.CRITICAL)
  return l

## 1) Application initialisation and simple demo:

# Create a root file logger (logger_instance='') 

root_log = init_file_logger() # get a root logger instance with INFO level using file "log.txt"
# the root logger will also log all messages from the other loggers

# create and use 2 different file loggers:
logger1 = init_file_logger('log1.txt',logger_instance="LOG1") # get a logger instance with INFO level using file "log1.txt"
logger1.info("msg 1 for log1.txt (also goes to root logger)")

logger2a = init_file_logger('log2.txt',"warning",logger_instance="LOG2")
logger2a.debug("msg 2 is dropped") # "debug" level is below "warning"
logger2a.critical("msg 3 for log2.txt  (also goes to root logger)")

## 2) This could be in a differnt module that runs later:

# All loggers are application global and can be used from any module.

import logging

# the second time we access LOG2, we don't initialize it again.
logger2b = logging.getLogger("LOG2") # logger2b is the same than logger2a
logger2b.critical("msg 4 for log2.txt again (also goes to root logger)")

# The instances are organized in a tree, identified by a dotted instance name.
# Messages to a specific instance also go to all parents and also to the root logger:
logger1sub = init_file_logger('log1sub.txt',logger_instance="LOG1.SUB")
logger1sub.info("msg 5 for log1sub.txt - also goes to log1.txt (and also to the root logger)")