simple encryption

gistfile1.py

from math import ceil
from itertools import izip_longest


def encrypt(s, w):
    n = len(s)
    l = [s[i:i + w] for i in xrange(0, n, w)]
    es = [''.join(t) for t in izip_longest(*l, fillvalue='')]
    return str(w) + ''.join(es)


def decrypt(s):
    k = int(s[0])
    s = s[1:]
    n = len(s)
    w = int(ceil(1. * n / k))
    full = k - (k * w - n)
    l, st = [], 0
    for i in xrange(k):
        ww = w if i < full else w - 1
        l.append(s[st:st + ww])
        st += ww
    es = [''.join(t) for t in izip_longest(*l, fillvalue='')]
    return ''.join(es)