Question

I am currently writing an API and an application which uses the API. I have gotten suggestions from people stating that I should perform logging using handlers in the application and use a "logger" object for logging from the API.

In light of the advice I received above, is the following implementation correct?

class test:
    def __init__(self, verbose):
        self.logger = logging.getLogger("test")
        self.logger.setLevel(verbose)
    
    def do_something(self):
        # do something
        self.logger.log("something")
        # by doing this i get the error message "No handlers could be found for logger "test"

The implementation i had in mind was as follows:

 #!/usr/bin/python

 """ 
 ....
 ....
 create a logger with a handler 
 ....
 ....

 """

 myobject = test()
 try:
     myobject.do_something()
 except SomeError:
     logger.log("cant do something")

I’d like to get my basics strong, I’d be grateful for any help and suggestions for code you might recommend I look up.

Thanks!

Answer 1

It’s not very clear whether your question is about the specifics of how to use logging or about logging exceptions, but if the latter, I would agree with Adam Crossland that log-and-swallow is a pattern to be avoided.

In terms of the mechanics of logging, I would make the following observations:

1. You don’t need to have a logger as an instance member. It’s more natural to declare loggers at module level using logger = logging.getLogger(__name__), and this will also work as expected in sub-packages.
2. Your call logger.log(“message”) would likely fail anyway because the log method has a level as the first argument, rather than a message.

You should declare handlers, and if your usage scenario is fairly simple you can do this in your main method or if __name__ == '__main__': clause by adding for example

logging.basicConfig(filename='/tmp/myapp.log', level=logging.DEBUG, 
                    format='%(asctime)s %(levelname)s %(name)s %(message)s')

and then elsewhere in your code, just do for example

import logging
logger = logging.getLogger(__name__)

once at the top of each module where you want to use logging, and then

logger.debug('message with %s', 'arguments') # or .info, .warning, .error etc.

in your code wherever needed.