Flatten an array of arbitrarily nested arrays of integers into a flat array of integers.

flatten.py

from typing import List


def flatten_list(items: List) -> List[int]:
    """
    Flatten an array of arbitrarily nested arrays of integers into a flat array of integers.
        e.g. [[1,2,[3]],4] -> [1,2,3,4].

    >>> nested: list = [[1, 2, [3, [4, 4, 8, [8, 8, 7]]]], 4, [], None]
    >>> expected: List[int] = [1, 2, 3, 4, 4, 8, 8, 8, 7, 4]
    >>> assert flatten_list(nested) == expected
    """
    flatten: List[int] = []

    for item in items:
        if isinstance(item, list):
            flatten.extend(flatten_list(item))
        elif isinstance(item, int):
            flatten.append(item)

    return flatten
 

test_flatten.py

from typing import List
from flatten import flatten_list

def test_flatten() -> None:
    nested: list = [[1, 2, [3, [4, 4, 8, [8, 8, 7]]]], 4, [], None]
    expected: List[int] = [1, 2, 3, 4, 4, 8, 8, 8, 7, 4]

    assert flatten_list(nested) == expected

    
if __name__ == "__main__":
    test_flatten()