Flatten input list of lists given by user and out put a flattened list.

array_flatten.py

import ast
import sys
import unittest


def flatten(items):
    """Generator for thwoing our items from list of lists."""
    for x in items:
        if isinstance(x, list):
            for sub_x in flatten(x):
                yield sub_x
        else:
            yield x


class TestFlatten(unittest.TestCase):
    """Unit tests for flatten method."""

    def test_empty_list(self):
        self.assertEquals(list(flatten('')), [])

    def test_list_of_lists(self):
        self.assertEquals(list(flatten([[1, 2, 3], [4, [5, 6]], [7], [8, [9]]])), [1, 2, 3, 4, 5, 6, 7, 8, 9])


class MustBeAListError(ValueError):
    pass


def main():
    input_list = input("Enter the list you want to flatten: ")
    if not input_list:
        return []
    if sys.version_info > (3, 0):
        input_list = ast.literal_eval(input_list)
    if type(input_list) is not list:
        raise MustBeAListError("Input to flatten must be a list.")
    flat_list_generator = flatten(input_list)
    return list(flat_list_generator)


if __name__ == '__main__':
    test_object = TestFlatten()
    test_object.test_empty_list()
    test_object.test_list_of_lists()
    print(main())

This can be run using python3 array_flatten.py