[Python-Dev] Using logging in the stdlib and its unit tests (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Wed Dec 8 11:03:09 CET 2010

On Wed, 8 Dec 2010 01:19:45 +0000 (UTC) Vinay Sajip <vinay_sajip at yahoo.co.uk> wrote:

Antoine Pitrou <solipsis pitrou.net> writes:

> > Why wouldn't it be the default for all logging calls ? Such special > cases don't really make things easy to remember. > One size doesn't fit all. Everything's documented reasonably well. If you use it often, you remember it. If you use it seldom, you might need to look things up.

My point is that the default behaviour should be helpful.

I would point out that logging is really the kind of thing people don't want to spend time with. I know it's not very gratifying for the module author (you!), but nobody expects (*) to have to first configure a logging library when they want to use a third-party library. They expect it to work and give useful error report by default.

(*) (not in the Python land anyway; Java might be different)

The defaults are I believe reasonably convenient, or at least not inconvenient:

1. If writing a library, add a NullHandler to the top-level logger of your library, don't add any other handlers by default (i.e. on import), document the names of the loggers you use. Otherwise, see the following.

First, you cannot call it a "default", since the library writer has to make it explicit. Second, I don't find that convenient at all. When I use a third-party lib I want the errors to be displayed, not silenced. I'm willing to bet that most people have the same expectation. Especially when prototyping, since you're not sure you've got everything right.

So, that's two problems:

There's a third problem with it:

For a comparison, the warnings module logs all warnings by default on stderr without requiring any a priori configuration. And that's what stderr is for (reporting errors).

2. If writing a simple script, prototyping etc. i.e. for casual use, use logging.debug(), logging.info() etc. That's easy enough and convenient enough for casual users to remember, I hope. All WARNING, ERROR and CRITICAL events in your code and in that of any libraries you use will be printed to sys.stderr.

Indeed, this is convenient. And that's what I'm arguing should be the default for all loggers, not just the top-level one. There's no reason that what is convenient for the root logger isn't for other loggers.

3. If slightly less than very casual use (e.g. you want to log to file, or want a specific message format), call basicConfig(). Just the one extra line to remember to do, hopefully not too inconvenient.

I know that one line sounds "not too inconvenient" since you are the library author and you are so used to it (and certainly like using it and spend a lot of time improving its features, which is good). I think most people, however, have different expectations (see beginning of this message).

4. For more advanced use, use programmatic configuration, fileConfig or dictConfig to specify a configuration. Convenience is inversely proportional to how involved the configuration is.

That I have already noticed :)

Regards

Antoine.

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