How to use logging library? (Implement logging in Python)

Question

I would like to apply logging library in a class to get reports from the different steps in my code and use info, debug or error functions and keep it in a logging file. In addition I want to use multiprocessing in my code as well. But I could not quite figure out how it works and should be set up, plus I have used it in a code and defined it as following

import logging 

logging.basicConfig(filename='logfile.log',level=logging.DEBUG)

it halted the code and prevents to terminate the process. I am wondering how it should be used in a class and stopped and closed the log file?!! Any help would be appreciated...

Answer 1

You may go through Good logging practice in python for getting more idea of logging module and get more detailed info from Python document.

Below is a basic example on how to use logging module, in which I am knowingly raising an exception:

import logging
log = logging.getLogger("mylog")
log.setLevel(logging.DEBUG)

formatter = logging.Formatter(
    "%(asctime)s %(threadName)-11s %(levelname)-10s %(message)s")
# Alternative formatting available on python 3.2+:
# formatter = logging.Formatter(
#     "{asctime} {threadName:>11} {levelname} {message}", style='{')

# Log to file
filehandler = logging.FileHandler("debug.txt", "w")
filehandler.setLevel(logging.DEBUG)
filehandler.setFormatter(formatter)
log.addHandler(filehandler)

# Log to stdout too
streamhandler = logging.StreamHandler()
streamhandler.setLevel(logging.INFO)
streamhandler.setFormatter(formatter)
log.addHandler(streamhandler)

# Test it
log.debug("Some message")
log.error("An error!")
try:
    something()
except:
    log.exception("An exception occured!")

In your debug.txt, you will get output as:

2011-01-18 12:07:24,943  MainThread  DEBUG      Some message
2011-01-18 12:07:24,943  MainThread  ERROR      An error!
2011-01-18 12:07:24,943  MainThread  ERROR      An exception occured!
Traceback (most recent call last):
  File "./logtest.py", line 17, in 
    something()
NameError: name 'something' is not defined