Python - Avoid passing logger reference between functions?

Question

I have a simple Python script that uses the in-built logging.

I'm configuring logging inside a function. Basic structure would be something like this:

#!/usr/bin/env python import logging import ...  def configure_logging():     logger = logging.getLogger("my logger")     logger.setLevel(logging.DEBUG)     # Format for our loglines     formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")     # Setup console logging     ch = logging.StreamHandler()     ch.setLevel(logging.DEBUG)     ch.setFormatter(formatter)     logger.addHandler(ch)     # Setup file logging as well     fh = logging.FileHandler(LOG_FILENAME)     fh.setLevel(logging.DEBUG)     fh.setFormatter(formatter)     logger.addHandler(fh)     return logger  def count_parrots():     ...     logger.debug??  if __name__ == '__main__':     logger = configure_logging()     logger.debug("I'm a log file")     parrots = count_parrots() 

I can call logger fine from inside __main__. However, how do I call logger from inside the count_parrots() function? What's the most pythonic way of handling configuring a logger like this?

Answer 1

You can either use the root (default) logger, and thus the module level functions logging.debug, ... or get your logger in the function using it. Indeed, the getLogger function is a factory-like function with a registry (singleton like), i.e. it always returns the same instance for the given logger name. You can thus get your logger in count_parrots by simply using

logger = logging.getLogger("my logger")  

at the beginning. However, the convention is to use a dotted hierarchical name for your logger. See http://docs.python.org/library/logging.html#logging.getLogger

EDIT:

You can use a decorator to add the logging behaviour to your individual functions, for example:

def debug(loggername):     logger = logging.getLogger(loggername)      def log_(enter_message, exit_message=None):         def wrapper(f):             def wrapped(*args, **kargs):                 logger.debug(enter_message)                 r = f(*args, **kargs)                 if exit_message:                     logger.debug(exit_message)                 return r             return wrapped         return wrapper     return log_  my_debug = debug('my.logger')  @my_debug('enter foo', 'exit foo') def foo(a, b):     return a+b 

you can "hardcode" the logger name and remove the top-level closure and my_debug.