I came across the fast inverse square root algorithm after reading about it on Quora, and I decided to take a stab at implementing it in Python 3.

fast_inv_sqrt.py

from struct import pack, unpack
def inv_sqrt(n: float) -> float:
    n_half = n / 2
    n_hex = hex(unpack('>l', pack('>f', n))[0])
    magic_num = '0x5f3759df'
    guess_int = int(magic_num, 16) - (int(n_hex, 16) >> 1)
    guess_float = unpack('>f', pack('>l', guess_int))[0]
    better_guess = guess_float*(1.5 - n_half*guess_float**2)
    return better_guess