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

On Thu, Jul 23, 2009 at 13:05, Guido van Rossum <guido@xxxxxxxxxx> wrote:

On Thu, Jul 23, 2009 at 12:09 PM, Fred Drake<fdrake@xxxxxxx> wrote:
> On Jul 23, 2009, at 2:59 PM, Georg Brandl wrote:
>>
>> is the presence of None values in sys.modules considered an implementation
>> detail? ÂIf not, it should be documented what the None values mean to the
>> interpreter.
>
> As I recall, they're an optimization. ÂBut since sys.modules is itself
> documented, and many applications actually use it, I think it's worth
> explaining that the None values can reasonably be expected, and what they
> indicate.

They should certainly be documented -- without them imports from
inside package would be super expensive (at least for Python versions
where implicit relative import exists). I'm somewhat surprised this
isn't documented, I don't think I've tried to keep this usage hidden.
I've also sometimes abused this to force some module to believe that a
certain other module doesn't exist.

It has not been hidden, but the only place I ever came across it was in the original essay about packages.

Â

OTOH in Py3k I'm not sure that we even *need* them any more, since
there is no more implicit relative import... They would only speed up
the raising of ImportError, not the finding of a similar-named module
elsewhere in the hierarchy.

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.

-Brett

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