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
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