+1! Thanks for pushing this. On Apr 15, 2012 4:04 AM, "Brett Cannon" <br...@python.org> wrote:
> To start off, what I am about to propose was brought up at the PyCon > language summit and the whole room agreed with what I want to do here, so I > honestly don't expect much of an argument (famous last words). > > In the "ancient" import.c days, a lot of import's stuff was hidden deep in > the C code and in no way exposed to the user. But with importlib finishing > PEP 302's phase 2 plans of getting imoprt to be properly refactored to use > importers, path hooks, etc., this need no longer be the case. > > So what I propose to do is stop having import have any kind of implicit > machinery. This means sys.meta_path gets a path finder that does the heavy > lifting for import and sys.path_hooks gets a hook which provides a default > finder. As of right now those two pieces of machinery are entirely implicit > in importlib and can't be modified, stopped, etc. > > If this happens, what changes? First, more of importlib will get publicly > exposed (e.g. the meta path finder would become public instead of private > like it is along with everything else that is publicly exposed). Second, > import itself technically becomes much simpler since it really then is > about resolving module names, traversing sys.meta_path, and then handling > fromlist w/ everything else coming from how the path finder and path hook > work. > > What also changes is that sys.meta_path and sys.path_hooks cannot be > blindly reset w/o blowing out import. I doubt anyone is even touching those > attributes in the common case, and the few that do can easily just stop > wiping out those two lists. If people really care we can do a warning in > 3.3 if they are found to be empty and then fall back to old semantics, but > I honestly don't see this being an issue as backwards-compatibility would > just require being more careful of what you delete (which I have been > warning people to do for years now) which is a minor code change which > falls in line with what goes along with any new Python version. > > And lastly, sticking None in sys.path_importer_cache would no longer mean > "do the implicit thing" and instead would mean the same as NullImporter > does now (which also means import can put None into sys.path_importer_cache > instead of NullImporter): no finder is available for an entry on sys.path > when None is found. Once again, I don't see anyone explicitly sticking None > into sys.path_importer_cache, and if they are they can easily stick what > will be the newly exposed finder in there instead. The more common case > would be people wiping out all entries of NullImporter so as to have a new > sys.path_hook entry take effect. That code would instead need to clear out > None on top of NullImporter as well (in Python 3.2 and earlier this would > just be a performance loss, not a semantic change). So this too could > change in Python 3.3 as long as people update their code like they do with > any other new version of Python. > > In summary, I want no more magic "behind the curtain" for Python 3.3 and > import: sys.meta_path and sys.path_hooks contain what they should and if > they are emptied then imports will fail and None in sys.path_importer_cache > means "no finder" instead of "use magical, implicit stuff". > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > http://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > http://mail.python.org/mailman/options/python-dev/anacrolix%40gmail.com > >
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