prime_factors.py

def generate_prime_factors(n):
    primes = []
    factor = 2
    while factor <= n:
        while n % factor == 0:
            primes.append(factor)
            n /= factor
        factor += 1
    return primes


# unit tests
import unittest

class TestPrimeFactors(unittest.TestCase):
    def test_one(self):
        self._assertPrimeFactors(1, [])

    def test_two(self):
        self._assertPrimeFactors(2, [2])

    def test_three(self):
        self._assertPrimeFactors(3, [3])

    def test_four(self):
        self._assertPrimeFactors(4, [2, 2])

    def test_six(self):
        self._assertPrimeFactors(6, [2, 3])

    def test_eight(self):
        self._assertPrimeFactors(8, [2, 2, 2])

    def test_nine(self):
        self._assertPrimeFactors(9, [3, 3])

    def _assertPrimeFactors(self, num, factors):
        self.assertEqual(generate_prime_factors(num), factors)


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