flattenlist.py

import unittest


def flatten(arg_list, result_list):
    """ Flatten an array of arbitrarily nested arrays of
        integers into a flat array of integers. """
    for x in arg_list:
        if isinstance(x, list):
            flatten(x, result_list)
        else:
            result_list.append(x)
    return result_list

# Tests

class TestFlatten(unittest.TestCase):

    def test_blank_list(self):
        self.assertTrue(flatten([], []) == [])

    def test_same_list(self):
        self.assertTrue(flatten([1,2,3,4], []) == [1,2,3,4])

    def test_single_nested_list(self):
        self.assertTrue(flatten([1,2,[3],4], []) == [1,2,3,4])

    def test_multiple_nested_list(self):
        self.assertTrue(flatten([1,2,[3],[4]], []) == [1,2,3,4])

    def test_complex_nested_list(self):
        self.assertTrue(flatten([[1,2,[3]],4], []) == [1,2,3,4])


if __name__ == '__main__':
    unittest.main()