[Python-Dev] requirements for moving __import__ over to importlib?

[Brett Cannon]

On Wed, Feb 8, 2012 at 11:09, Antoine Pitrou <solipsis at pitrou.net> wrote:

> Le mercredi 08 février 2012 à 11:01 -0500, Brett Cannon a écrit :
> >
> >
> > On Tue, Feb 7, 2012 at 17:42, Antoine Pitrou <solipsis at pitrou.net>
> > wrote:
> >         On Tue, 7 Feb 2012 17:24:21 -0500
> >         Brett Cannon <brett at python.org> wrote:
> >         >
> >         > IOW you want the sys.modules case fast, which I will never
> >         be able to match
> >         > compared to C code since that is pure execution with no I/O.
> >
> >
> >         Why wouldn't continue using C code for that? It's trivial
> >         (just a dict
> >         lookup).
> >
> >
> >  Sure, but it's all the code between the function call and hitting
> > sys.modules which would also need to get shoved into the C code. As I
> > said, I have not tried to optimize anything yet (and unfortunately a
> > lot of the upfront costs are over stupid things like checking if
> > __import__ is being called with a string for the module name).
>
> I guess my point was: why is there a function call in that case? The
> "import" statement could look up sys.modules directly.
>

Because people like to do wacky stuff  with their imports and so fully
bypassing __import__ would be bad.


> Or the built-in __import__ could still be written in C, and only defer
> to importlib when the module isn't found in sys.modules.
> Practicality beats purity.


 It's a possibility, although that would require every function call to
fetch the PyInterpreterState to get at the cached __import__ (so the proper
sys and imp modules are used) and I don't know how expensive that would be
(probably as not as expensive as calling out to Python code but I'm
thinking out loud).
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