Fast Inverse Square Root (Quake III) on Python

q_rsqrt.py

import struct

def q_rsqrt(number):
	i = 0
	x2 = 0.
	y = 0.

	threehalfs = 1.5
	x2 = number * 0.5
	y = number
	i = struct.unpack("I", struct.pack("f", y))[0]
	i = 0x5f3759df - (i >> 1)
	y = struct.unpack("f", struct.pack("I", i))[0]
	y = y * (threehalfs - (x2 * y * y))
	return y