I was attempting the patch for issue3125 to py3k, and in it Amaury
defines a new ForkingPickler:
from pickle import Pickler
class ForkingPickler(Pickler):
dispatch = Pickler.dispatch.copy()
This is also related to issue3350 I suspect. However, using the
pickle.Pickler module under py3k, there is no dispatch() method on the
class:
Trunk:
Python 2.6b1+ (trunk:65015M, Jul 16 2008, 10:15:51)
[GCC 4.0.1 (Apple Inc. build 5465)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> dir(pickle.Pickler)
['_BATCHSIZE', '__doc__', '__init__', '__module__', '_batch_appends',
'_batch_setitems', 'clear_memo', 'dispatch', 'dump', 'get', 'memoize',
'persistent_id', 'put', 'save', 'save_bool', 'save_dict',
'save_empty_tuple', 'save_float', 'save_global', 'save_inst',
'save_int', 'save_list', 'save_long', 'save_none', 'save_pers',
'save_reduce', 'save_string', 'save_tuple', 'save_unicode']
>>>
py3k:
Python 3.0b1+ (py3k:65011M, Jul 16 2008, 11:50:11)
[GCC 4.0.1 (Apple Inc. build 5465)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> dir(Pickler)
['__class__', '__delattr__', '__doc__', '__eq__', '__format__',
'__ge__', '__getattribute__', '__gt__', '__hash__', '__init__',
'__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__',
'__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__',
'bin', 'clear_memo', 'dump', 'fast', 'memo', 'persistent_id']
I think the fix for 3125 resolves your complaint in 3350, but is the
lack of the dispatch method intentional?
I ran into a few problems while trying to fix this issue. First, does
someone know how to add class attributes on extension types? It sounds
like I will need either some tp_dict hacking or a Pickler subclass.
Second, which methods of Pickler should be made public? I know
save_reduce() is needed, but would it be worthwhile to expose more? In
the recipe Amaury linked (which abuses Pickler IMHO), save_global(),
save_dict(), write() and memoize() are used. Exposing all save_* methods
is out of question for now as none were written to be used standalone.
Third, should Pickler allows pickling support for built-in types (e.g.,
int, dict, tuple, etc) to be overridden? Currently, pickle.py allows it.
However, I am not sure if it is a good idea to copy this "feature" in
_pickle.c.