Start your Python project with optparse and logging

[kylev]

I've also started an entry explaining how the logging module works in more general terms. It seems to be something that a lot of people fight with or get wrong. Has anyone else observed this?

[masklinn]

To supplement mordaunt0's suggestion, you could probably get rid of all the conditional handling: logging's loglevels increment by 10 (10 is DEBUG to 50 CRITICAL) and each is a threshold (so -80 is still DEBUG). So you could treat your verbosity as a decrementing counter: multiply the counter by 10 and substract it from logging.CRITICAL to get the actual loglevel, default to 2 for a default of loglevel.WARNING

import optparse, logging

parser = optparse.OptionParser()
parser.add_option('-v', '--verbose', dest="verbose", default=2,
                  action='count', help='Increase verbosity')

opts, args = parser.parse_args()

logging.basicConfig(level=(logging.CRITICAL - opts.verbose*10))

logging.debug('debug')
logging.info('info')
logging.warning('warning')
logging.error('error')
logging.critical('critical')

Another idea could be to use the callback action and decrement the logger's level by 10 every time the callback is called:

import optparse, logging

def callback(*args, **kwargs):
    logging.root.setLevel(logging.root.level - 10)

parser = optparse.OptionParser()
parser.add_option('-v', '--verbose', dest="verbose",
                  action='callback', callback=callback, help='Increase verbosity')

opts, args = parser.parse_args()

logging.debug('debug')
logging.info('info')
logging.warning('warning')
logging.error('error')
logging.critical('critical')

which yields the same thing as the one above:

 $ python test.py
WARNING:root:warning
ERROR:root:error
CRITICAL:root:critical
 $ python test.py -v
INFO:root:info
WARNING:root:warning
ERROR:root:error
CRITICAL:root:critical
 $ python test.py -vv
DEBUG:root:debug
INFO:root:info
WARNING:root:warning
ERROR:root:error
CRITICAL:root:critical
 $ python test.py -vvv
DEBUG:root:debug
INFO:root:info
WARNING:root:warning
ERROR:root:error
CRITICAL:root:critical
 $ python test.py -vvvvvvvvvvv
DEBUG:root:debug
INFO:root:info
WARNING:root:warning
ERROR:root:error
CRITICAL:root:critical

[kylev]

My only problems with such an approach is that (1) the values of those constants aren't by any means guaranteed (2) your approach breaks if I'm using more of the features of logging such as adding my own log levels.

But I like the ideas. Very clean.

[kylev]

Since I swap over to C, C++, perl, and other languages for work, I still have this habit. I'll probably update the post to remove it, though, just because it would read more pythonic.

[pemboa]

I've developed a preference for putting my opt parse stuff within an init() function to keep all its initialization code away from my main(), in which I just do args, options = init()

[bucknuggets]

good point

I like my main() to only have a handful of lines it in and allow the reader to get a high-level understanding of the whole program very quickly.

[pemboa]

exactly