Count non-zero bits

pop.py

def pop(x):
    x = int(x)
    x -= ((x >> 1) & int('0x55555555', 16))
    x = (x & int('0x33333333', 16)) + ((x >> 2) & int('0x33333333', 16))
    x = (x + (x >> 4)) & int('0x0F0F0F0F', 16)
    x += (x >> 8)
    x += (x >> 16)
    return x & int('0x0000003F', 16)

x = int('0b10111100011000110111110111111', 2)
print 'x =',
print x
print 'count non-zero bits in x'
print 'result is ' + str(pop(int('0b10111100011000110111110111111', 2)))


x = '1' * 32
x = int('0b' + x, 2)

print 'result is ' + str(pop(x))