Dear c-level python specialists,
Nested classes in python are really handy, and work pretty well,
except for a bug in pickling:
Let's define a nested class:
sage: class Bla:
....: class Ble:
....: pass
....:
Let's fake Bla is defined in a module, not in the interpreter:
sage: import __main__
sage: __main__.Bla = Bla
Dumping an element of Bla works just fine:
sage: x = Bla()
sage: dumps(x)
"x\x9ck`\xd2H\x8e\x8f\xcfM\xcc\xcc\x8b\x8f\xe7r\xcaI\xe4*d\xcc/d\xaa-dN\xd2\x03\x00v\xe3\x08'"
But dumping an element of Bla.Ble breaks:
sage: x = Bla.Ble()
sage: dumps(x)
---------------------------------------------------------------------------
PicklingError Traceback (most recent call
last)
/home/nthiery/.sage/temp/zephyr/23765/_home_nthiery__sage_init_sage_0.py in
<module>()
/opt/sage/local/lib/python2.5/site-packages/sage/structure/sage_object.so in
sage.structure.sage_object.dumps (sage/structure/sage_object.c:5539)()
PicklingError: Can't pickle __main__.Ble: attribute lookup __main__.Ble
failed
>
/opt/sage-3.4.rc0/devel/sage-combinat/sage/sage_object.pyx(571)sage.structure.sage_object.dumps
(sage/structure/sage_object.c:5539)()
---------------------------------------------------------------------------
The reason behind this is twofold:
First, the name of the class is improperly set:
sage: Bla.Ble
<class __main__.Ble at 0xb1e7c98c>
sage: Bla.Ble.__name__
'Ble'
(which btw probably breaks other tools around)
Well, let's work around this:
sage: Bla.Ble.__name__ = "Bla.Ble"
But then, a second problem: the code of cPickle (around line 1977)
tries to lookup the attribute "Bla.Ble" in __main__, instead of
successively looking up "Bla" in __main__, and then "Ble" in the result:
sage: dumps(Bla.Ble)
---------------------------------------------------------------------------
PicklingError Traceback (most recent call
last)
/home/nthiery/.sage/temp/zephyr/23765/_home_nthiery__sage_init_sage_0.py in
<module>()
/opt/sage/local/lib/python2.5/site-packages/sage/structure/sage_object.so in
sage.structure.sage_object.dumps (sage/structure/sage_object.c:5539)()
PicklingError: Can't pickle __main__.Bla.Ble: attribute lookup
__main__.Bla.Ble failed
>
/opt/sage-3.4.rc0/devel/sage-combinat/sage/sage_object.pyx(571)sage.structure.sage_object.dumps
(sage/structure/sage_object.c:5539)()
It would take me a couple hours to learn the syntax to write c-code
for python modules. Could any of the experts out there write me a
2-line patch upon cPickle:1977 to do the right thing (i.e. split
__name__, and make the attribute lookup for each bit)? Just a draft
will be fine; I am fine with reading and simple debuging.
Thanks in advance!
Best regards,
Nicolas
Here is the broken code:
mod = PyImport_ImportModule(module_str);
if (mod == NULL) {
cPickle_ErrFormat(PicklingError,
"Can't pickle %s: import of module %s "
"failed",
"OS", args, module);
goto finally;
}
############### HERE ####################
klass = PyObject_GetAttrString(mod, name_str);
if (klass == NULL) {
cPickle_ErrFormat(PicklingError,
"Can't pickle %s: attribute lookup %s.%s "
"failed",
"OSS", args, module, global_name);
goto finally;
}
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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