[Python-Dev] PEP 420 - dynamic path computation is missing rationale

[Eric V. Smith]

> Here's another suggestion: instead of modifying the finder/loader code
> to pass these names through, assume that we can always find
> (module_name, attribute_name) with this code:
> 
> def find_parent_path_names(module):
>     parent, dot, me = module.__name__.rpartition('.')
>     if dot == '':
>         return 'sys', 'path'
>     return parent, '__path__'
> 
>>>> import glob
>>>> find_parent_path_names(glob)
> ('sys', 'path')
>>>> import unittest.test.test_case
>>>> find_parent_path_names(unittest.test.test_case)
> ('unittest.test', '__path__')
> 
> I guess it's a little more fragile than passing in these names to
> NamespaceLoader, but it requires less code to change.
> 
> I think I'll whip this up in the pep-420 branch.

I tried this approach and it works fine. The only caveat is that it
assumes that the parent path can always be computed as described above,
independent of what's passed in to PathFinder.load_module(). I think
that's reasonable, since load_module() itself hard-codes sys.path if the
supplied path is missing.

I've checked this in to the pep-420 branch. I prefer this approach over
Nick's because it doesn't require any changes to any existing
interfaces. The changes are contained to the namespace package code and
don't affect other code in importlib.

Assuming this approach is acceptable, I'm done with the PEP except for
adding some examples.

And I'm done with the implementation except for adding tests and a few
small tweaks.

Eric.