cPickle: adds support for class pickling customization

[nthiery]

Original implementation:

The first patch imports the vanilla cPickle.c and test_cpickle.py
from python 2.5.2.p9 as sage.misc.cPickle, and updates accordingly the
cPickle imports throughout the sage library.

The second patch makes a very small modification to cPickle to allow
for customizing how class are pickled via metaclasses.

Final implementation: adds the second patch to the python spkg

See discussions on:

• http://groups.google.com/group/comp.lang.python/browse_thread/thread/66c282afc04aa39c/
• http://groups.google.com/group/sage-devel/browse_thread/thread/583048dc7d373d6a/

Thanks to Mike, Burcin, and Carl for suggestions on how to handle this.

CC: @sagetrac-sage-combinat @sagetrac-cwitty @saliola @burcin @craigcitro

Component: misc

Keywords: cPickle, pickling classes

Author: Craig Citro, Nicolas M. Thiéry

Reviewer: Craig Citro, Nicolas M. Thiéry

Merged: sage-4.2.alpha0

Issue created by migration from https://trac.sagemath.org/ticket/5985

[nthiery]

Description changed:

--- 
+++ 
@@ -1 +1,12 @@
+The first patch imports the vanilla cPickle.c and test_cpickle.py
+from python 2.5.2.p9 as sage.misc.cPickle, and updates accordingly the
+cPickle imports throughout the sage library.
 
+The second patch makes a very small modification to cPickle to allow
+for customizing how class are pickled via metaclasses.
+
+See discussions on:
+- http://groups.google.com/group/comp.lang.python/browse_thread/thread/66c282afc04aa39c/
+- http://groups.google.com/group/sage-devel/browse_thread/thread/583048dc7d373d6a/
+
+

[nthiery]

Description changed:

--- 
+++ 
@@ -9,4 +9,4 @@
 - http://groups.google.com/group/comp.lang.python/browse_thread/thread/66c282afc04aa39c/
 - http://groups.google.com/group/sage-devel/browse_thread/thread/583048dc7d373d6a/
 
-
+Thanks to Mike, Burcin, and Carl for suggestions on how to handle this.

[nthiery]

comment:6

I just rebased the first patch upon 3.4.2 final. Please ignore (or better delete) the old version cPickle-5985-import.patch

[nthiery]

comment:7

Note: the cPickle imports in dsage will need to be updated as well.

[nthiery]

comment:8

Updated patch:

• Fixes a trivially failing doctest (don't know why I did not see them earlier)
• Adds some more doctest

[sagetrac-mabshoff]

comment:10

This patch needs an explicit addition of sage/misc/cPickle.c to MANIFEST.in for -sdist to work. It is also listed to have a positive review in the CategoriesRoadMap, but it isn't on the ticket.

Cheers,

Michael

[robertwb]

comment:11

Followup at #5986