Workaround mishandled nested classes in Python and cPickle

[nthiery]

With the python code below::
class A:
class B:
pass
Python 2.6 erroneously set the B.name to "B" instead of "A.B".

Furthermore, upon pickling (here in save_global)
and unpickling (in load_global) a class
with name "A.B" in a module mod, the standard
cPickle module searches for "A.B" in mod.dict
instead of looking up "A" and then "B" in the result.

This patch works around this by a patch to cPickle.c (in fact a copy of it in the Sage source tree; see #5985) which fixes the name for B to its appropriate value A.B, and inserts 'A.B' = A.B in
mod.dict (hacky, but seems to work) the first time A.B is pickled,
and fixes load_global to implement a proper lookup upon unpickling.

It also ensures that sage/interfaces/sage0.py uses loads/dumps from
sage_object rather than calling directly cPickle.loads/dumps
(+1 by cwitty on this change)

Python source experts are more than welcome to rework/rewrite this patch!

Depends on #5483 and #5985

CC: @sagetrac-sage-combinat @sagetrac-cwitty

Component: misc

Keywords: nested classes

Author: Craig Citro, Nicolas M. Thiéry

Reviewer: Robert Bradshaw

Merged: sage-4.2.alpha0

Issue created by migration from https://trac.sagemath.org/ticket/5986

[nthiery]

comment:2

Attachment: cPickle-5986-nested-classes-submitted.patch.gz

[robertwb]

comment:4

This workaround it a bit to hackish for my taste, but it's been implemented and tested. Followup at #6121.

[jasongrout]

comment:5

Replying to @robertwb:

This workaround it a bit to hackish for my taste, but it's been implemented and tested. Followup at #6121.

Does that mean that this ticket can be closed?

[nthiery]

comment:6

Replying to @jasongrout:

Replying to @robertwb:

This workaround it a bit to hackish for my taste, but it's been implemented and tested. Followup at #6121.

Does that mean that this ticket can be closed?

Not before Robert or someone else writes a proof of concept patch upon the category code proving that #6121 is a usable replacement for this one to get pickling to work for parents and categories.
See discussion on Sage devel.

[nthiery]

Author: Nicolas M. Thiéry

[nthiery]

Attachment: trac_5986-use-nested_class_metaclass.patch.gz

Apply only this one

[nthiery]

comment:7

The newly attached patch implements a completely different fix, using #6110 and #6121.

William is ok integrating this in 4.1.2 if it's ready on time (see IRC).

Robert: please review! (unless you feel you should be an author, and get someone else to review it :-))

[nthiery]

Changed author from Nicolas M. Thiéry to Craig Citro, Nicolas M. Thiéry

[nthiery]

Reviewer: Robert Bradshaw

[robertwb]

comment:8

Much less intrusive--too bad we didn't pursue this just a bit more back in June.

[mwhansen]

Merged: sage-4.2.alpha0