Hinting specific types for attributes in subclasses where parent can have many types-CodePudding

I have a parent class Foo which has an attribute bar. It has two subclasses which each have bar as a different type: FooStr has bar as a str, and FooInt has bar as an int. Foo is an abstract base class.

How can I hint the specific type of an attribute in subclasses where the parent can have many types?

This is what I started with. The hinting for the subclasses FooStr and FooInt tells me bar is a union of str or int, not very useful.

class Foo(abc.ABC):
    def __init__(self, bar: typing.Union[str, int], stuff):
        self.bar = bar
        self.stuff = stuff

class FooStr(Foo):
    pass

class FooInt(Foo):
    pass

Next I tried hinting the types in the init methods of the subclasses, but the hinting for bar in the subclasses still shows the type as a union.

class Foo(abc.ABC):
    def __init__(self, bar: typing.Union[str, int], stuff):
        self.bar = bar
        self.stuff = stuff

class FooStr(Foo):
    def __init__(self, bar: str, stuff):
        super().__init__(self, bar, stuff)

class FooInt(Foo):
    def __init__(self, bar: int, stuff):
        super().__init__(self, bar, stuff)

Then I tried removing bar from the parent init which hints the correct types for the subclasses, but not defining bar in the parent class Foo seems incorrect to me.

class Foo(abc.ABC):
    def __init__(self, stuff):
        self.stuff = stuff

class FooStr(Foo):
    def __init__(self, bar: str, stuff):
        self.bar = bar
        super().__init__(self, stuff)

class FooInt(Foo):
    def __init__(self, bar: int, stuff):
        self.bar = bar
        super().__init__(self, stuff)

Not sure where to go from here...

CodePudding user response：

Use the Generic base class, you can then pass the variable type when subclassing your parent class

from typing import Generic, TypeVar


T = TypeVar('T')


class Foo(Generic[T]):
    def __init__(self, bar: T, stuff):
        self.bar = bar
        self.stuff = stuff


class FooStr(Foo[str]):
    pass


class FooInt(Foo[int]):
    pass