square_root.py

# python 2.7+
from itertools import dropwhile, tee, izip

def repeatfunc(f, zero):
    curr = zero
    while 1:
        yield curr
        curr = f(curr)

def pairwise(origin):
    a, b = tee(origin)
    next(b, None)
    return izip(a,b)

def snd(origin):
    it = origin if hasattr(origin, "next") else iter(origin)
    next(it, None)
    return next(it, None)

def square_root(n, eps=0.01):
    def f(x): return (x + float(n)/x)/2
    def outside((left, right)): return abs(left-right) > eps
    return snd(next(dropwhile(outside, pairwise(repeatfunc(f, n)))))