flattener.py

import unittest

def flatten(arr):
    """ Write some code, that will 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].
    """
    flattened_arr = []
    def recur(el):
        if type(el) == list:
            for e in el:
                recur(e)
        elif type(el) == int:
            flattened_arr.append(el)
        else:
            raise TypeError('List elements must be integers or lists')
    recur(arr)
    return flattened_arr


class TestFlattener(unittest.TestCase):
    print(flatten([[1,2,[3]],4]))

    def test_flatten(self):
        """ Test that the flattener works correctly
        """
        test_arr = [[1,2,[3]],4]
        res = flatten(test_arr)
        self.assertEqual(res, [1,2,3,4])

    def test_error(self):
        """ Test that the appropriate exception gets raised on bad input
        """
        with self.assertRaises(TypeError) as te:
            flatten([[1,{'hello': 'world'},['a']],4])

        self.assertEqual(type(te.exception), TypeError)


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