Incorrect pickling behavior in the c implemented classmethod descriptors #95196
Description
Bug report
Hello there, this is my first bug report so apologies if there's something I miss.
Consider the following code:
import pickle classmethod_descriptor = dict.__dict__["fromkeys"] unpickled_classmethod_descriptor = pickle.loads(pickle.dumps(classmethod_descriptor, protocol=5)) While it passes without raising any errors, classmethod_descriptor differs from unpickled_classmethod_descriptor. Instead of the original descriptor, the pickling process yields the function itself:
>>> classmethod_descriptor <method 'fromkeys' of 'dict' objects> >>> unpickled_classmethod_descriptor <function dict.fromkeys(iterable, value=None, /)> Manually calling the descriptor's __reduce_ex__ allows us to see the reason:
>>> classmethod_descriptor.__reduce_ex__(5) (<function getattr>, (dict, 'fromkeys')) This behavior differs from python implemented classmethods:
import pickle class A: @classmethod def method(cls): pass classmethod_descriptor = A.__dict__["method"] # Any of these lines will raise "TypeError: cannot pickle 'classmethod' object" pickle.dumps(classmethod_descriptor, protocol=5) classmethod_descriptor.__reduce_ex__(5) Since it fails with normal classmethods, I would expect it to fail with their c counterparts as well so their behavior would match.
Either that, or having both of them succeed during the pickling process, in which case, __reduce_ex__ should return a valid result in both cases.
The bug occurs with other c implemented class methods as well:
import pickle from datetime import datetime classmethod_descriptor = datetime.__dict__["now"] # Returns False pickle.loads(pickle.dumps(classmethod_descriptor, 5)) == classmethod_descriptor # Returns True pickle.loads(pickle.dumps(classmethod_descriptor, 5)) == datetime.now Your environment
Python Versions:
I've tested it with both 3.10.5 and 3.11.04b
OS - Windows 10 Pro 64 bit