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

[Brett Cannon]

On Fri, Jul 24, 2009 at 10:58, Guido van Rossum <guido at python.org> wrote:

> On Fri, Jul 24, 2009 at 10:50 AM, Brett Cannon<brett at python.org> wrote:
> >
> >
> > On Fri, Jul 24, 2009 at 10:39, Guido van Rossum <guido at python.org>
> wrote:
> >>
> >> Still works, at least in some old 3.1 I had lying around:
> >>
> >> $ python3.1
> >> Python 3.1a0 (py3k:70152, Mar  3 2009, 16:55:42)
> >> [GCC 4.0.1 (Apple Inc. build 5465)] on darwin
> >> Type "help", "copyright", "credits" or "license" for more information.
> >> >>> import sys
> >> >>> sys.modules['string'] = None
> >> >>> import string
> >> Traceback (most recent call last):
> >>  File "<stdin>", line 1, in <module>
> >> ImportError: No module named string
> >> >>>
> >> $ python3.1
> >> Python 3.1a0 (py3k:70152, Mar  3 2009, 16:55:42)
> >> [GCC 4.0.1 (Apple Inc. build 5465)] on darwin
> >> Type "help", "copyright", "credits" or "license" for more information.
> >> >>> import string
> >> >>>
> >> $
> >>
> >> The experiment should be easily repeatable. :-)
> >
> > =) Yes, the None raising ImportError semantics can be added easily and
> > codified as official import semantics in 3.1.
>
> I thought it was too simple. :-) Maybe I should go back to bed and
> nurse my cough some more instead of playing hookie from being sick and
> indulging in email.
>

I'm glad I can help provide a distraction. And I hope you get over whatever
you have soon.


>
> > I was talking about the "None
> > triggers another import as with relative imports" semantics and if there
> was
> > some rather convoluted way to trigger that.
>
> I can't think of one and doubt you will find one -- it was introduced
> (in the earliest of early package import implementations) to optimize
> the problem we had with code living inside a package trying to stat()
> a toplevel module locally each time an import of it was processed (a
> problem if a package contains lots of modules each of which import os,
> sys, etc.). Since we no longer to relative import, I don't see how
> there could be another use -- if it's not there it's not there.
>
> > I am guessing not as that would
> > require a value of -1 for level which is no longer valid.
>
> Ah. Sure.
>
> > I will fix importlib in both 3.2 and 3.1.1. And speaking of fixing,
> should I
> > put the failing test in now and decorate it with unittest.expectedFailure
> > until I get around to fixing it?
>
> Oh, I don't know. All this new-fangled technology... Can't you just
> leave it in your workspace, unsubmitted, until you get to fixing it?
>

Oh sure, I normally just leave it in my scratch svn checkout until I get
around to it. But since we now have the decorator I was wondering if any
discussion came up while I was gone of using it within our
tests when we happen to get a working (failing) test case before we
have a patch to fix it.

-Brett
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