Bug report

The behavior of partialmethod changed in python3.11. This caused a library that I use testsuite to fail.

Here is a minimal use case that demonstrates this:

from functools import partialmethod


class Cell:
    def __init__(self):
        self.alive = False

    def set_state(self, state):
        self.alive = bool(state)


class Wrapper:
    def set_state_wrap(self, cell: Cell, state):
        cell.set_state(state)


wrapper = Wrapper()

Cell.set_alive = partialmethod(wrapper.set_state_wrap, True)

cell = Cell()
cell.set_alive()
print(cell.alive)

In python3.10, this prints True. In python3.11 it errors with:

Traceback (most recent call last):
  File "/home/gary/partialmethod.py", line 23, in <module>
    c.set_alive()
TypeError: Wrapper.set_state_wrap() missing 1 required positional argument: 'state'

The arguments passed to Wrapper.set_state_wrap are:
python3.10: wrapper, cell, True
python3.11: cell, True

So partialmethod is forgetting that set_state_wrap is a method of wrapper, and it needs to pass that in as the first arg.

I know that the way that they are using partialmethod here is not how it is intended to be used, and feels wrong. However this change is behavior if intended should be documented.

Your environment

• CPython versions tested on: Python 3.11.0 (broken) Python 3.10.7 (working)
• Operating system and architecture: Fedora Linux 36