具有元类注册的数据类

Question

我有一个数据类A，它可以被继承并用于创建其他类。每当我的类A继承时，我都希望将子类注册到容器中。我想用元类解决它，但是对我来说不起作用。有什么帮助吗？

container = {}

class Meta(type):
    def __new__(mcs, *args, **kwargs):
        new_class = super().__new__(mcs, *args, **kwargs)

        if new_class.__name__ != 'A':
            container[new_class.__name__] = new_class

        return new_class


@metaclass
class MasterClass:
    parent


@metaclass
class A(MasterClass, metaclass=Meta):
    my_arg


@metaclass
class Child(A): # <-- this class I would like to register into child container
    my_next_arg

Answer 1

您的代码几乎是正确的，但是当使用“ @metaclass”作为“ @dataclass”修饰符，并在字段上创建一些注释时，没有NameError异常。

所以，如果您只是这样做：

from dataclasses import dataclass
from typing import Any
container = {}

class Meta(type):
    def __new__(mcs, *args, **kwargs):
        new_class = super().__new__(mcs, *args, **kwargs)

        if new_class.__name__ != 'A':
            container[new_class.__name__] = new_class

        return new_class


@dataclass
class MasterClass:
    parent: Any


@dataclass
class A(MasterClass, metaclass=Meta):
    my_arg: Any


@dataclass
class Child(A): # <-- this class I would like to register into child container
    my_next_arg: Any

它将按您期望的方式工作，并且Child将被注册到容器：

In [5]: container                                                                                                                    
Out[5]: {'Child': __main__.Child}

只需注意，从Python 3.6开始，您不需要使用元类对于此模式，称为__init_subclass__类方法关于子类的创建，并且可以做到相同：

from dataclasses import dataclass
from typing import Any

container = {}

@dataclass
class MasterClass:
    parent: Any


@dataclass
class A(MasterClass):
    def __init_subclass__(cls, *args, **kw):
        super().__init_subclass__(*args, **kw)
        container[cls.__name__] = cls

    my_arg: Any


@dataclass
class Child(A): # <-- this class I would like to register into child container
    my_next_arg: Any