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

On Thu, Jul 23, 2009 at 20:18, Guido van Rossum <guido@xxxxxxxxxx> 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.

Â

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

Â

--Guido

On Thu, Jul 23, 2009 at 7:50 PM, Brett Cannon<brett@xxxxxxxxxx> wrote:
>
>
> On Thu, Jul 23, 2009 at 19:48, Benjamin Peterson <benjamin@xxxxxxxxxx>
> wrote:
>>
>> 2009/7/23 Brett Cannon <brett@xxxxxxxxxx>:
>> >
>> >
>> > On Thu, Jul 23, 2009 at 19:38, Benjamin Peterson <benjamin@xxxxxxxxxx>
>> > wrote:
>> >>
>> >> 2009/7/23 Brett Cannon <brett@xxxxxxxxxx>:
>> >> > 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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