create filesystem-safe places for url-keyed data to be stored

def chunk(url):
    """ create filesystem-safe places for url-keyed data to be stored """
    chunks = lambda l, n: [l[x: x+n] for x in xrange(0, len(l), n)]
    url_64 = base64.urlsafe_b64encode(url)
    return chunks(url_64, 255)