Python 3.12中的通用[T]类方法隐式类型检索

如果您阅读typing.py的源代码，您会看到Generic的类型参数存储为Base Class _BaseGenericAlias的__args__属性.请注意，这是一个未记录的实现细节.

然后，当该方法用classmethod子类装饰(标记了特殊属性的函数)时，我们只需要修补其代理属性getter _BaseGenericAlias.__getattr__，以将额外的关键字参数注入到具有包装器函数的方法调用中:

class TypeArgsClassMethod(classmethod):
    def __get__(self, obj, obj_type=None):
        method = super().__get__(obj, obj_type)
        method.__func__._inject_type_args = True
        return method

def __getattr__(self, name):
    if hasattr(obj := orig_getattr(self, name), '_inject_type_args'):
        @wraps(obj)
        def wrapper(*args, **kwargs):
            return obj(*args, __type_args__=self.__args__, **kwargs)
        return wrapper
    return obj

if _BaseGenericAlias.__getattr__ is not __getattr__:
    orig_getattr = _BaseGenericAlias.__getattr__
    _BaseGenericAlias.__getattr__ = __getattr__

以便:

class MyClass[T]:
    kind: type[T]

    @TypeArgsClassMethod
    def make_class(cls, __type_args__) -> "MyClass[T]":
        print(__type_args__)
        return cls()

MyClass[int].make_class()

输出:

(<class 'int'>,)

演示 here

或者，您可以将自定义类方法重新绑定到Generic类型，以便类方法的第一个参数将成为Generic类型.内置types.MethodType不允许更新__self__以进行重新绑定，因此您必须定义Python-equivalent version:

from functools import update_wrapper
from typing import _BaseGenericAlias

class MethodType:
    def __init__(self, func, obj):
        self.__func__ = func
        self.__self__ = obj

    def __call__(self, *args, **kwargs):
        func = self.__func__
        obj = self.__self__
        return func(obj, *args, **kwargs)

class GenericClassMethod:
    def __init__(self, f):
        self.f = f
        update_wrapper(self, f)

    def __get__(self, obj, cls=None):
        if cls is None:
            cls = type(obj)
        method = MethodType(self.f, cls)
        method._generic_classmethod = True
        return method

def __getattr__(self, name):
    if hasattr(obj := orig_getattr(self, name), '_generic_classmethod'):
        obj.__self__ = self
    return obj

if _BaseGenericAlias.__getattr__ is not __getattr__:
    orig_getattr = _BaseGenericAlias.__getattr__
    _BaseGenericAlias.__getattr__ = __getattr__

以便您可以访问类型参数的__args__属性，以及原始类的__origin__属性:

class MyClass[T]:
    kind: type[T]

    @GenericClassMethod
    def make_class(cls) -> "MyClass[T]":
        print(cls)
        print(cls.__origin__)
        print(cls.__args__)

MyClass[int].make_class()

This 输出:

__main__.MyClass[int]
<class '__main__.MyClass'>
(<class 'int'>,)

演示 here