[Python-Dev] Document None values in sys.modules?

[Brett Cannon]

On Thu, Jul 23, 2009 at 20:18, Guido van Rossum <guido at python.org> wrote:

> So, I guess, we'll live with it for a while longer. Given that it
> managed to evade our attention for so long, I think that's fine.
>

Can someone double-check me that the semantics can even be triggered in 3.1?
I just tried and couldn't come up with anything. Heck, I quick search for a
Py_None comparison in 3.1's import.c turned up nothing useful (other than
mark_miss() is the function used to set None in sys.modules). We might have
actually already removed it or made it so that the semantics can't be
triggered.


>
> I agree that there's no reason for a None result from loaders to be
> interpreted the same way, assuming that's not how it works ATM.
>
> And we can live with import and importlib differing on this in 3.1
> (though you could call it a bug in importlib and fix it for 3.1.1 --
> not sure if you were planning on that).
>

I can if people can trigger the semantics somehow so I have a test to go by.

-Brett


>
> --Guido
>
> On Thu, Jul 23, 2009 at 7:50 PM, Brett Cannon<brett at python.org> wrote:
> >
> >
> > On Thu, Jul 23, 2009 at 19:48, Benjamin Peterson <benjamin at python.org>
> > wrote:
> >>
> >> 2009/7/23 Brett Cannon <brett at python.org>:
> >> >
> >> >
> >> > On Thu, Jul 23, 2009 at 19:38, Benjamin Peterson <benjamin at python.org
> >
> >> > wrote:
> >> >>
> >> >> 2009/7/23 Brett Cannon <brett at python.org>:
> >> >> > None in Python 3.1 is really useless in terms of its semantics in
> >> >> > relative
> >> >> > imports; importlib doesn't support it and still passes as
> __import__
> >> >> > (at
> >> >> > least last time I ran the test suite that way). I thought we had
> >> >> > agreed
> >> >> > a
> >> >> > while back that supporting None was not warranted in Python 3.0?
> >> >> > Otherwise I
> >> >> > will do whatever work is necessary for this to happen.
> >> >>
> >> >> I think it's still nice for the rare cases where you need to trick a
> >> >> module into thinking another one doesn't exist.
> >> >
> >> > But None does not strictly mean "I don't exist". None is supposed to
> >> > trigger
> >> > an another import attempt for the module with a top-level name. It's
> >> > that
> >> > extra import trigger that has no real use in 3.0 and just complicates
> >> > import
> >> > semantics (IMO) needlessly. If you want a module to not exist then you
> >> > either stick something else in (e.g. '42') or we remove the special
> >> > semantics for None (which I thought we had).
> >>
> >>
> >> I didn't realize None had other semantics attached to it. (Imagine
> >> that dealing with import!) +1 for making it simply indicate an
> >> ImportError.
> >
> > I'm +0 with having import raise ImportError if None is set in sys.modules
> as
> > long as we don't suddenly expect loaders to trigger the same thing if
> they
> > return None (actually, as of right now what loaders return count for
> > nothing, but just want to be clear).
> > -Brett
>
>
>
> --
> --Guido van Rossum (home page: http://www.python.org/~guido/)
>
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