#!/usr/bin/env python

def rle_8b(buf):
    acc = 1
    ret = []
    n = len(buf)
    i = 1
    while i < n:
        if buf[i] != buf[i - 1]:
            ret.append((acc, buf[i - 1]))
            acc = 1
        if buf[i] == buf[i - 1]:
            if acc == 2**8 - 1:
                # NOTE: the rationale for doing that is to later decode the
                # file (it's easier if you know on how many bits the length is
                # encoded). You don't have to dot it.
                ret.append((acc, buf[i]))
                acc = 1
            else:
                acc += 1
        i += 1
    ret.append((acc, buf[i - 1]))
    return ret

buf1 = "fjesffffffflllllljf"
buf2 = "fehs1111233"
buf3 = 256 * "a" + 512 * "C"

print("rle_8b({0}) → {1}".format(buf1, rle_8b(buf1)))
print("rle_8b({0}) → {1}".format(buf2, rle_8b(buf2)))
print("rle_8b({0}) → {1}".format(buf3, rle_8b(buf3)))