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

从 issue 中的复现开始，检查 Lib/unittest/mock.py 第 1637 行附近的恢复逻辑。比较当删除操作改变所观察到的值时，patch 如何处理没有 dict 的对象上的属性。完成标准是示例将 p.a 恢复为 True，同时保留普通对象的现有行为，并在相关的 unittest.mock 测试中添加回归测试覆盖。