patch does not correctly restore state on objects without __dict__

Bug report

Bug description:

from unittest.mock import patch
class Proxy(object):
    config = {}
    def __getattr__(self, name):
        return self.config[name]
    def __setattr__(self, name, value):
        if name == 'config':
            object.__setattr__(self, name, value)
            return
        self.config[name] = value
    def __delattr__(self, name):
        self.config[name] = 'DEFAULT'

p = Proxy()
p.a = True
print(p.a)
with patch('__main__.p.a', False):
    print(p.a)
print(p.a)

Expected

True
False
True

Actual

True
False
DEFAULT

Note that this is a relatively niche issue, but for example in a config system (i.e. https://github.com/pytorch/pytorch/pull/140779), if you don't want to have a delete work, (i.e. have it set it back to a default value), the code in https://github.com/python/cpython/blob/94a7a4e22fb8f567090514785c69e65298acca42/Lib/unittest/mock.py#L1637 will call delattr, and then not call setattr, because it still has the attr.

Possible fixes:
If delattr throws (maybe NotImplementederror), call setattr instead (this is nice and explicit + removes the hacky workaround I have to do).

If the value after it's been deleted doesn't equal the original value, reassign it? (this might require objects to be comparable, not sure if that is already an issue here).

Either way I wanted to see if there was any interest in fixing this, and if anyone saw a solution that seemed reasonable enough.

CPython versions tested on:

3.12

Operating systems tested on:

Linux

issue の再現から始め、Lib/unittest/mock.py の 1637 行付近にある復元ロジックを調べてください。削除によって観測される値が変わる場合に、patch が dict を持たないオブジェクトの属性をどのように処理するかを比較してください。完了条件は、例で p.a が True に復元され、通常のオブジェクトに対する既存の動作が維持され、関連する unittest.mock テストに回帰テストのカバレッジが追加されていることです。