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

[Eric V. Smith]

On 05/22/2012 09:49 PM, PJ Eby wrote:
> On Tue, May 22, 2012 at 8:40 PM, Eric V. Smith <eric at trueblade.com
> <mailto:eric at trueblade.com>> wrote:
> 
>     On 5/22/2012 2:37 PM, Guido van Rossum wrote:
>     > Okay, I've been convinced that keeping the dynamic path feature is a
>     > good idea. I am really looking forward to seeing the rationale added
>     > to the PEP -- that's pretty much the last thing on my list that made
>     > me hesitate. I'll leave the details of exactly how the parent path is
>     > referenced up to the implementation team (several good points were
>     > made), as long as the restriction that sys.path must be modified in
>     > place is lifted.
> 
>     I've updated the PEP. Let me know how it looks.
> 
> 
> My name is misspelled in it, but otherwise it looks fine.  ;-)

Oops, sorry. Fixed (I think).

>     I have not updated the implementation yet. I'm not exactly sure how I'm
>     going to convert from a path list of unknown origin to ('sys', 'path')
>     or ('foo', '__path__'). I'll look at it later tonight to see if it's
>     possible. I'm hoping it doesn't require major surgery to
>     importlib._bootstrap.
> 
> 
> It shouldn't - all you should need is to use
> getattr(sys.modules[self.modname], self.attr) instead of referencing a
> parent path object directly.

The problem isn't the lookup, it's coming up with self.modname and
self.attr. As it currently stands, PathFinder.find_module is given the
parent path, not the module name and attribute name used to look up the
parent path using sys.modules and getattr.

Eric.