What does this error mean: "TypeError: Parameters to generic types must be types"?

Question

I'm not sure what this error means:

TypeError: Parameters to generic types must be types. Got slice(typing.List, <class 'int'>, None).

I am trying to confirm if a matrix has a given cell/index in it. (In matrix [[A, B, C], [D, E, F]] does cell/index [0, 2] exist? Yes at C).

My input parameter is a list specifying the cell's index. I want to take the cell/list and modify it to check if it exists. Every time I try to touch the parameter list, it gives the error.

def in_matrix(matr: List[List:int], cell: List[int]) -> bool:
    b = cell.pop()
    a = cell.pop()
    print(a)
    print(b)
    for y in range(len(matr)):
        for x in range(len(matr[y])):
            if matr[a][b] == True:
                return True
            else:
                return False

Answer 1

This type matr: List[List:int] should be matr: List[List[int]] (in Python >= 3.9 you can even just use matr: list[list[int]]).

This means that matr is a list of integer lists, like:

matr = [[1, 2, 3],
        [4, 5, 6],
        [7, 8, 9]]