def countBits(self, num: int) -> List[int]: meaning code example

Example 1: nums: List[int] in python function

from typing import List
Vector = List[float]

def scale(scalar: float, vector: Vector) -> Vector:
    return [scalar * num for num in vector]

# typechecks; a list of floats qualifies as a Vector.
new_vector = scale(2.0, [1.0, -4.2, 5.4])

Example 2: nums: List[int] in python function

"""
In the function greeting, the argument name is expected to be of type str and the 
return type str. Subtypes are accepted as arguments.
"""
def greeting(name: str) -> str:
    return 'Hello ' + name