Bitwise operations in Python

bitwise.py

import unittest


def lsb(i):
    """Return the position of the first (lowest) bit that's set."""
    if not i:
        return 0

    count = 1
    while i:
        if i & 0x1:
            return count
        i = i >> 1
        count += 1
    return 0


def popcount(i):
    """Return the number of bits that are set."""
    if not i:
        return 0

    count = 0
    while i:
        if i & 0x1:
            count += 1
        i = i >> 1
    return count


class LsbTest(unittest.TestCase):
    def testLsb(self):
        #                              4321
        self.assertEqual(0, lsb(0))  # 0000
        self.assertEqual(1, lsb(1))  # 0001
        self.assertEqual(2, lsb(2))  # 0010
        self.assertEqual(1, lsb(3))  # 0011
        self.assertEqual(3, lsb(4))  # 0100


class PopCountTest(unittest.TestCase):
    def testPopCount(self):
        self.assertEqual(0, popcount(0))  # 0000
        self.assertEqual(1, popcount(1))  # 0001
        self.assertEqual(1, popcount(2))  # 0010
        self.assertEqual(2, popcount(3))  # 0011
        self.assertEqual(1, popcount(4))  # 0100
        self.assertEqual(2, popcount(5))  # 0101
        self.assertEqual(2, popcount(6))  # 0110
        self.assertEqual(3, popcount(7))  # 0111


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