Should python debug statements etc be wrapped by if debug?

Question

Coming from Java, it is advisable to wrap a log.debug with

if (log.isDebugEnabled())
    log.debug("blah blah blah "+someObject+" more blahs than you can blah at"):

Is there a similar reson to do this in python? Or does python handle strings differently?

Out of curiosity, *why* is it advisable? Maybe then we could tell you if those reasons apply to Python. — , Jun 28 '13 at 09:53
Is there a ... yes! Here, an SO question for java: http://stackoverflow.com/questions/963492/in-log4j-does-checking-isdebugenabled-before-logging-improve-performance. Effectively, it is a typical simple performance optimization. Ugh, i guess my trivial example wasn't quite right... let me fix — bharal, Jun 28 '13 at 09:55
@bharal, thanks for clarifying what do you really mean - I've updated the answer, recheck it, please. — alecxe, Jun 28 '13 at 11:36

score 3 · Answer 1 · answered Apr 24 '16 at 12:08

The suggested answer ignores the overhead of string concatenation and any heavy method calls.

So this:

log.debug("blah blah blah "+someObject+" more blahs than you can blah at")

Will cost the string contact, even in ERROR logging level.

Different languages/loggers manage that in different ways, checking for isDebugEnabled() or isEnabledFor() are good best practices.

Of course, you shouldn't pre-optimize if this is not relevant, like anything in this world.

alecxe · Accepted Answer · 2013-06-28T11:35:53.357

There is no need for additional checks. Just configure your logging level:

>>> import logging
>>> root = logging.getLogger()
>>> root.setLevel(logging.INFO)
>>> root.addHandler(logging.StreamHandler())
>>> logging.error("test")
test
>>> logging.debug("test")
>>>

Again, there is no need for additional checks (the source code taken from logging/__init__.py):

class Logger(Filterer):
    ...
    def debug(self, msg, *args, **kwargs):
        """
        Log 'msg % args' with severity 'DEBUG'.

        To pass exception information, use the keyword argument exc_info with
        a true value, e.g.

        logger.debug("Houston, we have a %s", "thorny problem", exc_info=1)
        """
        if self.isEnabledFor(DEBUG):
            self._log(DEBUG, msg, args, **kwargs)

As you can see logging itself makes the check.

Hope that helps.

Just found this on the hunt for python equivalent ifdef debug; exactly what i needed. — Stephen Murby, Jul 11 '14 at 08:16

Should python debug statements etc be wrapped by if debug?

2 Answers2