10-2.py

s = '1321131112'

for n in xrange(0, 50):
    chains = []
    chain = s[0]
    prev = s[0]

    part = s[1:]
    for index, c in enumerate(part, start=1):
        if c == prev:
            chain += c
        else:
            chains.append(chain)
            chain = c
            prev = c
        if index == len(part):
            chains.append(chain)

    s = ''.join(['{}{}'.format(len(item), item[0]) for item in chains])
    print 'done loop', n

print len(s)