Square rooter

def squirtle(n):
    i = 1
    while i * i < n:
        i += 1

    a, b = float(i), float(n) / i
    for i in xrange(0, 2**7):
        a, b = (a + b) / 2, float(n) / a

    return b

print "%.16f" % (squirtle(2), )