[Python-Dev] new import hooks & zip import

[Guido van Rossum]

> Skip Montanaro wrote:
> 
> > Scanning the patch summary I see:
> > 
> >     sys.path_hooks is a list of callable objects that take 
> >     a string as their only argument. A hook will be called 
> >     with a sys.path or pkg.__path__ item. It should return 
> >     an "importer" object (see below), or raise ImportError 
> >     or return None if it can't deal with the path item. By 
> >     default, sys.path_hooks only contains the zipimporter 
> >     type, if the zipimport module is available. 
> > 
> > Why have it raise ImportError or return None if it can't deal with the path
> > item?  Shouldn't there be only one way to report failure?  (Or do I misread
> > your explanation?)
> 
> No, you read correctly... I'm not sure, I just thought if might be
> convenient to also be able to return None. I'd be happy to stick
> with just one way, though (which would be raising ImportError, as
> that's easiest from __init__ methods).

Hm, I'd prefer None.  With an exception (especially when you're
reusing an existing exception) you never know if it was raised
intentionally or whether it means a real (unexpected) error -- in the
latter case, swallowing the traceback would be a bad idea because it
makes diagnosing the real problem hard.  ("Why does my zipimport not
work?  I don't get any errors, but it doesn't work...")

--Guido van Rossum (home page: http://www.python.org/~guido/)