[IPython-dev] strange namespace issue

[Darren Dale]

On Friday 14 September 2007 2:50:23 am you wrote:
> On 9/11/07, Darren Dale <dd55 at cornell.edu> wrote:
> > These are the specific changes that are causing some trouble. I dont
> > quite follow what is being done here. Is a module being injected into the
> > namespace, or is the entire namespace being overwritten? This post I
> > pointed out earlier
> > (http://osdir.com/ml/web.zope.devel/2004-02/msg00051.html) might still be
> > relevant. Maybe the new code is overwriting an important namespace
> > reference, and should instead be updating it?
[...]
> As it turns out, my changes were having problems because now this is
> done using a real module object (which is good, since it lets for
> example doctest work).  But when the Python interpreter tears down a
> module object, it resets *in place* all its members to None,

I thought it might be something like this...

> regardless of who may be holding a reference to it.  

but this is surprising behavior to me.

> That's where all 
> those weird None errors were coming from, as I fell in a trap already
> described by a much better pen than me:
>
>     I stand amid the roar
>     Of a surf-tormented shore,
>     And I hold within my hand
>     Grains of the golden sand-
>     How few! yet how they creep
>     Through my fingers to the deep,
>     While I weep- while I weep!
>     O God! can I not grasp
>     Them with a tighter clasp?
>     O God! can I not save
>     One from the pitiless wave?
>     Is all that we see or seem
>     But a dream within a dream?

Well said, my philosopher!

> I just committed a solution that's not the most elegant (holding a
> private reference to these things), but that I think should work
> correctly, and doesn't create any more of a major memory penalty than
> we already have anyway.
>
> These changes are a bit delicate and they touch the very core of user
> code execution, so more testing from all the willing is *really
> needed*.
>
> So please, go forth and reproduce bugs...

Nice work, Fernando. Thank you for tracking this down.

Darren