listFlattener.py

def listFlattener(arg, *args, **kwargs):
    """ Flattens a deeply nested list of integers. But only integers! """
    output = list()

    # check input type
    if type(arg) != list:
        raise Exception('Invalid input type. Only accepts list')

    def extract_elements(input):
        for i in input:
            if type(i) == int:
                output.append(i)
            elif type(i) == list:
                # recurs if element is a list
                extract_elements(i)
            else:
                raise Exception(
                    'Invalid data type encountered : ' + i + ' : ' + str(type(i)))

    extract_elements(arg)
    return output


if __name__ == "__main__":
    # if this program is called directly run some tests

    test_input_1 = [[[[1,[2, [[[[90]]]]],3,4,5]]]]
    test_output_1 = listFlattener(test_input_1)
    if test_output_1 == [1,2,90,3,4,5]:
        print('Test-1 passed')
    else:
        print('Test-1 failed')