[Python-3000] Interest in PEP for callbacks on module import

[Nick Coghlan]

Phillip J. Eby wrote:
>> > Does anyone else think this is an issue worth pursuing?
> 
> A qualified yes: the Importing package took a long time to get correct 
> under all the crazy little twists and turns of importing, including 
> correctly handling things like the link between packages and their child 
> packages/modules, the import order of same, race conditions, import 
> locks, clearing out callbacks, etc.  I'm somewhat hesitant as to whether 
> a from-scratch reimplementation is wise.

I'm far from convinced that a from-scratch rewrite (particularly in C) 
is a great idea myself - that's why I suggested a PEP to look at some of 
the issues.

Some curly questions I thought of myself:

- What do we do if something is inserted in sys.modules directly, and 
then imported later? Do registered callbacks for that module trigger at 
all? If so, when?

- Does the lazy importing code need to reacquire the import lock before 
loading the module on attribute access?

> There may be other interop issues with libraries that use ModuleType 
> subclasses or do lazy import, deprecation, and similar module content 
> manipulation, so a publicized PEP would be a good idea to get their 
> developers' input.

Yeah, the more I think about it, the more I think a new PEP for lazy and 
weak importing is the right way to go (although it would be nice if 
using the latter didn't automatically cause the former). I'll put an 
initial draft together (unless someone else beats me to it - I almost 
certainly won't find time to do it until after Christmas)

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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