How should I annotate a function returning a ctypes array in Python?

Question

Consider the following Python code:

def foo(aqs : typing.List[int]) -> ??? :
    array_type = ctypes.c_int64 * len(aqs)
    ans = array_type(*aqs)
    return ans

What's the correct annotation for the return value of this function? (In place of ???)

Answer 1

This function doesn't have a consistent return type, since the length of the returned array is part of the array's type. However, the type is always a subclass of ctypes.Array, which is the most specific annotation you can use:

def foo(aqs: List[int]) -> ctypes.Array:
    ...