[Python-Dev] New and Improved Import Hooks (original) (raw)

Just van Rossum just@letterror.com
Tue, 3 Dec 2002 17:39:36 +0100

Moore, Paul wrote:

That's great news, as I've said before. Can I ask that you consider a few issues, though. I don't have particular use cases in mind, but I believe that PEP 273 had a number of implicit assumptions, which your proposal does not incorporate. I'd like to make the differences explicit, just so that people get a chance to comment on whether they care.

1. Your import hooks seem to act at a level "above" sys.path, in the sense that the normal sys.path search becomes just another hook. With that in mind, I don't see a way for a user to add a zipfile in the middle of sys.path.

True. There would be ways around that, but it's currently not easy. I don't feel this is a particularly important feature, though.

2. The syntax needed to add a zipfile search is different from the familiar one for sys.path additions. This isn't an issue as such, but may make the feature a little less accessible.

The way I see it: sys.path is for file system imports. It's a list of directories, nothing else.

3. By using a non-sys.path approach, you make it impossible for users to set PYTHONPATH to include zipfiles.

This could be fixed by site.py: it could remove any .zip files from sys.path and add hooks for them in sys.import_hooks. Or it could be fixed in the C code that adds the script's directory to sys.path. Or we could add a tiny change to import.c that invokes the zipimport module if a zip file is encountered.

[ snip ]

> It adds > a whole directory listing caching scheme that is a) totally > unneeded and b) has (IMO) nothing to do with zip importing > per se. That ExternalNames/External names stuff? I don't > understand why it is needed just to enable zip imports. It's a > lot of stuff!

I've explained this a couple of times now. Please read the PEP for details, but Jim claims that zipfile imports need this if they are not to be too slow.

Well, I am not going to need it: upon reading the zip contents table I build a dict, mapping (full) module names to toc info. One dict lookup will be enough to get at the right data.

Let's discuss the rest when my implementation actually works.

Just