[Python-Dev] PEP 382 progress: import hooks

[P.J. Eby]

At 01:51 PM 7/22/2010 +0100, Martin v. Löwis wrote:
>At EuroPython, I sat down with Brett and we propose an approach
>how namespace packages get along with import hooks. I reshuffled
>the order in which things get done a little bit, and added a
>section that elaborates on the hooks.
>
>Basically, a finder will need to support a find_path method,
>return all .pth files, and a loader will need to support a
>load_module_with_path method, to initialize __path__.
>
>Please comment if you think that this needs further changes;

I'm not certain I understand it precisely.  There seem to be some 
ambiguities in the spec, e.g.:

"If fullname is not found, is not a package, or does not have any 
*.pth files, None must be returned."

What does "is not a package" actually mean in that context?  What 
happens if an empty list is returned - does that mean the importer is 
saying, "this is a package, whether it has an __init__.py or not?"

As for the "list of strings" returned, is each string the entire 
contents of the .pth file?  Is it to be \n-separated, or is any 
universal-newlines-compatible string accepted?  Is there a particular 
order in which .pth file contents are to be returned?

Regarding load_module_with_path(), how does its specification differ 
from simply creating a module in sys.modules, setting its __path__, 
and then invoking the standard load_module()?  (i.e., is this method 
actually needed, since a correct PEP 302 loader *must* reuse an 
existing module object in sys.modules)


>I'll hope to start implementing it soon.

Am I correct in understanding that, as written, one would have to 
redefine __import__ to implement this in a library for older Python 
versions?  Or is it implementable as a meta_path importer?


>Regards,
>Martin

Thanks for your work on this, I was just thinking about pinging to 
see how it was going.  ;-)

(I want setuptools 0.7 to be able to supply an add-on module for 
supporting this PEP in older Pythons, so that its current .pth hacks 
for implementing namespace packages can be dropped.)