How do I use type hint for multiple classes in a dictionary but they inherit from same parent class?

Question

I want to use type hint with string as a key and different classes as a value in a dictionary like below.

configurations: Dict[str, what_class??] = {
    "dev": Dev,
    "product": Product,
    "test": Test,
}

The classes Dev, Product, Test inherit from a base class "Parent".

class Parent:
    pass

class Dev(Parent):
    pass

class Product(Parent):
    pass

class Test(Parent):
    pass

What is the best way to do the type hint for this?

Do I need to set just "Any" as their type?

Does this answer your question? [Subclass in type hinting](https://stackoverflow.com/questions/46092104/subclass-in-type-hinting) — Marius ROBERT, Jun 21 '22 at 07:25
@MariusROBERT the answer you linked gave me a hint to think about this situation but the most accurate answer was the one from Ron Serruya. It was good to read the answer to get a hint. — Eric Lee, Jun 21 '22 at 08:28

score 1 · Answer 1 · answered Jun 21 '22 at 07:27

In your case, creating a dictionary without using type hints seems the most optimal solution, as you can access all classes directly from the dict variable configurations, using the proper string key value:

class Parent:
    pass

class Dev(Parent):
    pass

class Product(Parent):
    pass

class Test(Parent):
    pass

configurations = {
    "dev": Dev,
    "product": Product,
    "test": Test,
}

print(configurations)

Output:

{'dev': <class '__main__.Dev'>, 'product': <class '__main__.Product'>, 'test': <class '__main__.Test'>}

Also, using the Parent class works well if you still want to use type hints:

import typing
class Parent:
    pass

class Dev(Parent):
    pass

class Product(Parent):
    pass

class Test(Parent):
    pass

configurations: typing.Dict[str, Parent] = {
    "dev": Dev,
    "product": Product,
    "test": Test,
}
print(configurations)

It outputs the same dictionary as the above code.

What do you mean by "without using type hints seems the most optimal solution"? is your view to type hinting is optional? — Eric Lee, Jun 21 '22 at 08:34
@eric-lee I just proposed it as another solution, which I consider the best. However, I don't know the full project that is behind that solution. — Cardstdani, Jun 21 '22 at 08:35
I see. I just wanted to implement type hinting for my code looking better for others. Thanks for the advices. — Eric Lee, Jun 22 '22 at 01:48

score 1 · Accepted Answer · answered Jun 21 '22 at 07:32

Depends on how accurate you want your hints to be,

Use the parent class

configurations: Dict[str, Parent] = {
    "dev": Dev,
    "product": Product,
    "test": Test,
}

Specify the classes in a union

from typing import Union
configurations: Dict[str, Union[Dev, Product, Test]] = {
    "dev": Dev,
    "product": Product,
    "test": Test,
}

Create a TypedDict type for this specific dict

from typing import TypedDict

class EnvDict(TypedDict):
    dev: Dev
    product: Product
    test: Test
    
configurations: EnvDict = {
    "dev": Dev,
    "product": Product,
    "test": Test,
}

Seems like the third one was the answer I was looking for! – Eric Lee Jun 21 '22 at 08:29 — Eric Lee, Jun 21 '22 at 08:29

How do I use type hint for multiple classes in a dictionary but they inherit from same parent class?

2 Answers2