main.py

#!/usr/bin/env python

"""
Another fun python variable manipulation question is: given an int, write a one
liner that returns the string representation of the int, but with a comma every
three decimal places starting from the right. (i.e., 1 return "1", and 1000
returns "1,000")

(Rules: the one line cannot use anything that has to be imported, and cannot use
any string formatting)

http://python.reddit.com/comments/15z6xg/q/c7re8uf
"""

import unittest

def stringify_with_commas(the_int):
    return ''.join(str(the_int)[::-1][i:i+3] + ',' for i in range(0, len(str(the_int)), 3))[::-1][1:]

class TestSequenceFunctions(unittest.TestCase):

    def setUp(self):
        self.func = stringify_with_commas

    def test_one(self):
        self.assertEqual(self.func(1), '1')

    def test_one_thousand(self):
        self.assertEqual(self.func(1000), '1,000')

    def test_one_million(self):
        self.assertEqual(self.func(1000000), '1,000,000')

    def test_one_million_and_change(self):
        self.assertEqual(self.func(1234567), '1,234,567')

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