a way to get the type of a variable

[DetachHead]

in my use case if have a class with several generics, i want a convenient way to get the type of an instance, but it doesn't seem to be possible in any type checkers

from typing import Generic, TypeVar

T = TypeVar("T")

class Foo(Generic[T]):
    ...

foo = Foo[int]()
bar = Foo[str]()

baz: type[foo] | type[bar] = ...

mypy errors:

main.py:11: error: Variable "__main__.foo" is not valid as a type
main.py:11: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
main.py:11: error: Variable "__main__.bar" is not valid as a type

the alternative is to duplicate the types (which is annoying if the type annotation is large) or create a type alias, which is a pain

in typescript you can use typeof

interface Foo<T> {}

declare const foo: Foo<number>
declare const bar: Foo<string>

declare const baz: typeof foo | typeof bar

PS: i tried baz: reveal_type(foo) = foo, but no luck

[erictraut]

I think you've already identified the workarounds that are available in Python today:

1. Specify the type explicitly within the annotation
2. Define a type alias and use that in the annotation

I wouldn't expect type[foo] to work. The equivalent of TypeScript's typeof foo would be type(foo). Currently that's not allowed because call expressions are not permitted within type annotation expressions. There are good reasons for that limitation, and (speaking as a type checker maintainer) I'd recommend that we leave that limitation in place and not create an exception.

This use case is not common, so it's reasonable that you create a type alias in this circumstance.

[srittau]

I believe this is a duplicate of #769.