Python Class Mutex via MRO

mutex_class.py

from typing import Callable
from random import choices
from itertools import permutations
registry: dict[type, tuple[type, Callable, Callable]] = {} # old: (new, ori_init, ori_init_subclass)
rev_registry: dict[type, type] = {}
__lock: bool = False
__inner: bool = False

def get_latest_from_reg(cls: type):
    while cls in registry:
        cls = registry[cls][0]
    return cls

def new_init(v: type, *args, **kwargs): # old
    r = registry[v][1](*args, **kwargs)
    args[0].__class__ = get_latest_from_reg(v) # registry[v][0]
    return r

def is_subcls_unmod(cls: type):
    class __internal: ...
    return type(cls.__init_subclass__) == type(__internal.__init_subclass__)

def new_init_subclass(v: type, cls: type, *args, **kwargs): # old, unmod_subclass?
    global __lock, __inner
    try:
        __set_inner = False
        if not __inner:
            ori_cls = cls
            cls = get_latest_from_reg(cls)
            v = get_latest_from_reg(v)
            __inner = True
            __set_inner = True
            try:
                __lock = True
                mro = tuple(map(get_latest_from_reg, cls.mro()))
                new_cls = type(cls.__name__, mro, {})
            finally:
                __lock = False
            ori_init = ori_cls.__init__
            ori_init_subclass = ori_cls.__init_subclass__
            cls.__init__ = init_closure(cls)
            cls.__init_subclass__ = init_subclass_closure(cls)
            registry[cls] = (new_cls, ori_init, ori_init_subclass)
            rev_registry[new_cls] = cls
            if is_subcls_unmod(ori_cls):
                return ori_init_subclass(*args, **kwargs)
            else:
                return ori_init_subclass.__func__(cls, *args, **kwargs)
    finally:
        if __set_inner:
            __inner = False

def init_closure(v: type):
    def inner(*args, **kwargs):
        return new_init(v, *args, **kwargs)
    inner.__name__ = "__init__"
    inner.__qualname__ = v.__qualname__
    return inner

def init_subclass_closure(v: type):
    def inner(cls, *args, **kwargs):
        return new_init_subclass(v, cls, *args, **kwargs)
    inner.__name__ = "__init_subclass__"
    inner.__qualname__ = v.__qualname__
    return classmethod(inner)

def factorial(x):
    t = 1
    for v in range(1, x+1): t *= v
    return t

def as_mutex(*t):
    global __inner
    size = 1
    while factorial(size) < len(t): size += 1
    rnd = "".join(choices("0123456789abcdef", k=16))
    prefix = "__Mutex_" + "_".join(map(lambda x: x.__name__, t)) + "_" + rnd + "_"
    mutex = [type(f"{prefix}_{i}", (), {}) for i in range(size)]
    for curr, mutex_comb in zip(t, permutations(mutex, len(mutex))):
        ori_curr = curr
        curr = get_latest_from_reg(curr)
        reso = tuple(curr.mro()[:-1] + list(mutex_comb) + [object])
        try:
            __inner = True
            new_cls = type(curr.__name__, reso, {}) #  + "_mutex_" + rnd
        finally:
            __inner = False
        ori_init = ori_curr.__init__
        ori_init_subclass = ori_curr.__init_subclass__
        curr.__init__ = init_closure(curr)
        curr.__init_subclass__ = init_subclass_closure(curr)
        registry[curr] = (new_cls, ori_init, ori_init_subclass)
        rev_registry[new_cls] = curr


if __name__ == '__main__':
    class A:...
    class B:...
    as_mutex(A, B)
    class C(A):...
    C()
    class D:
        def __init__(self, t):
            self.t = 1
    as_mutex(A, B, D)
    class E(D):
        def __init__(self, t):
            super().__init__(t)
            self.t
    E(1)
    class F:
        def __init_subclass__(cls):
            print(cls)

    as_mutex(A, B, F)
    class G(D, F): ...
    print(G(1).__class__.mro())
    try:
        class H(B, F): ...
        raise AssertionError
    except TypeError:
        ...

What the fuck? 😭😭😭

It basically modify the __init__ and __init_subclass__, so that they would be redirected for handling the modification.
On creating the mutex system, the minimal amount of mutex class is used (calculated by the factorial, which for x mutex, it have x! to arrange the class in different order)
It then gives each class a new inheritance of different ordered mutex, such that if 2 class being inherit at the same time, no valid MRO order can be form for the mutex.
For example

class A:...
class B:...
as_mutex(A, B)
A().__class__.mro() # [A_mod, A_ori, __Mutex_A_B__0, __Mutex_A_B__1, object]
B().__class__.mro() # [B_mod, B_ori, __Mutex_A_B__1, __Mutex_A_B__0, object]

Which therefore when you attempt to inherit A and B at the same time, Python MRO rule would lead to no valid way to resolved an order of method resolution (i.e. should __Mutex_A_B__0 be first or __Mutex_A_B__1 because they claim differently

You can noted that I do A().__class__.mro() instead of A.mro(), and the above MRO result shown A_mod and A_ori, this is because the class inheritance of A is not the one that changed, but the __init__ is injected such that the class of the object (via obj.__class__ = ...) would be replaced to the class with the mutex. The A_mod and A_ori is only for pure demonstration purpose, in which in the code, you would just see 2 A.
Strictly, injecting the __init__ is not necessary as the MRO check is being done before hand, but it would be really difficult to demonstrate the mutex so the __init__ injection is kept.

As the class inheritance of A and B isn't modified, how does it prevent it?
It was done by injecting the classmethod __init_subclass__, where it would check the initial MRO of the class, and then create a new class that contain the mutex, then inject the __init__ and __init_subclass__ so the cycle continues.