[Python-Dev] Solving the import-deadlock case

[Nick Coghlan]

On 3 Jul 2013 05:44, "R. David Murray" <rdmurray at bitdance.com> wrote:
>
> On Tue, 02 Jul 2013 20:31:48 +0200, Pascal Chambon <pythoniks at gmail.com>
wrote:
> > I agree that a module loading should be, as much as possible, "side
> > effects free", and thus shouldn't have temporary errors. But well, in
> > practice, module loading is typically the time where process-wide
> > initialization are done (modifying sys.path, os.environ, instantiating
> > connection or thread pools, registering atexit handler, starting
> > maintenance threads...), so that case has chances to happen at a moment
> > or another, especially if accesses to filesystem or network (SQL...) are
> > done at module loading, due to the lack of initialization system at
> > upper levels.
>
> There may well be a bug that could be/should be fixed here, but...it
> seems to me that other than the sys.path modifications, doing any of that
> at module import time has a strong code smell.

Unfortunately it's one of those "Your code is dubious, but so many people
do it anyway we should handle it better than we do" cases.

We could also be a lot more emphatic about "import side effects are what
marks the boundary between a library and a framework. To stay on the
library side of that fence provide a 'start' or 'configure' function
instead of doing things implicitly on import".

Heck, even *defining* library, framework and application would be a good
thing.

OTOH, it's hard to find motivation to work on improving the handling of
things you think people shouldn't be doing in the first place (that's one
of the reasons circular import handling has never been made more
consistent).

(That's not to dismiss the work Pascal's already done - just pointing out
why it may sometimes feel like it's difficult to get interest and feedback
on things like this).

Cheers,
Nick.

>
> --David
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