如何创建类型“等于”int的类？

Question

我正在尝试创建一个数据类，它可以从类型定义生成clickhouse（SQLISH）模式

例如，clickhouse支持：

• Int8
• Int16
• Uint8
• Uint16

在python中，这些类型不存在（afaik）。只是int。我希望我仍然可以创建一个类型结构，让我来表达它，并自动生成所需的模式，也许还可以对类型进行验证。我还希望当我传递int类型的值时，我的类型提示（我使用PyCharm，不确定mypy）不会抱怨

到目前为止，这是我的想法：

@dataclass
class ClickhouseType:
    @classmethod
    def schema_type(cls):
        return cls.__name__

    @classmethod
    def validate(cls, value):
        # just included as an example, not important as part of this discussion :) 
        pass


@dataclass
class Int8(int, ClickhouseType):
    @classmethod
    def validate(cls, value):
        # just included as an example, not important as part of this discussion :)
        assert -128 <= value <= 127

@dataclass
class MySchema:
    some_number: Int8


x = MySchema(some_number=4)  # type hint complaints that I pass an int when an Int8 is required

有没有办法让python/my-type-hinter明白我希望Int8可以与int互换

Answer 1

尝试使用直接继承创建类型：

class int8 (int):
    def __new__ (cls, value):
        assert -128<=value<=127
        return int(value) # Simplified
        # Or if you need more things:
        self = int.__new__(cls, value)
        self.something = "something else"
        return self

根据shadowranger的评论提示进行编辑：

Everything here will be type(int(...))==type(int8(...))==True, except the classes
__name__ attribute after instancing. And int8().__class__ of course.
Remember that the __new__() constructor is called before anything else in the class is "considered objectified". Therefore before the __init__() as well. __init__() is called after the object's construction, while __new__() is called practically before it.
__new() receives the class as a first argument, while __init__() receives already constructed object.
So, if multiple inheritance is used, some of initialization should go to __new__(), mostly those modifying the data type, and some of it should be done in __init__().

Note that type(int)!=type(int8)==True here, so this is not really an exact answer to your question, but it should be a good pointer combined with what you already know.