用户定义的类型显式声明一个嵌套类型

Question

I find it really useful to have Python types such as Dict[str, int] , which declare the types they contain and allow them to be type checked too. However I can't find how I can create such a type. If, for example, I write

    class Classy:
       def __init__(self, x: Any) -> None:
           self.value = x

how can I express it as Classy[int] , Classy[str] , Classy[List[int]] , etc?

Answer 1

Use TypeVar() to declare type variable, and use Generic as base class.

from typing import TypeVar, Generic
T = TypeVar('T')
class Classy(Generic[T]):
    def __init__(self, x: T) -> None:
        self.value = x
    def get_value(self) -> T:
        return self.value

You can try:

class1 = Classy[int](100)
class2 = Classy[str]('abc')
print(class1.get_value())
print(class2.get_value())

Then you will see:

100
abc