[Python] Is it possible to type a list of tuples of identical generic types, with a static...

Consider the following:

from typing import TypeVar, Generic

class A(): pass
class B(A): pass
class C(A): pass


T = TypeVar("T", bound=A)


class Container(Generic[T]):
def __init__(x: T):
pass

b: Container = Container(B())
c: Container[C] = Container(C())


How do I type-hint a function foo that will accept any list of tuples of identically typed containers:

foo([
(b, b),
(c, c)
])


but refuse this (heterogeneous tuple):

foo([
(c, b), # tuples elements are not the same type
(c, c)
])


I tried this:

ListOfSameContainerTuples = list[tuple[Container[T], Container[T]]]

def foo(containers: ListOfSameContainerTuples[T]):
pass


but it doesn't work:

foo([
(b, b),
(c, c)
])
# error: Argument 1 to "foo" has incompatible type "list[tuple[object, object]]";
# expected "list[tuple[Container[<nothing>], Container[<nothing>]]]" [arg-type]

foo([
(c, b),
(c, c)
])
# error: List item 0 has incompatible type "tuple[Container[C], Container]"; expected "tuple[Container[C], Container[C]]" [list-item]


The second error on mypy looks good, but I don't understand the first one:

• Why does mypy not know the type of b and c ?
• Why is my type signature Container[<nothing>] ?

I tried solutions from Tuple with multiple numbers of arbitrary but equal type, to no avail.

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