count char runs in a string

count_runs.py

#
# Which would be easier to extend and generalize for top N instead of max, and infinite s1?
#

s1 = 'aabbbbcbbaab'

nmax = 0
nwrd = 0
cmax = ''
prev = ''

for c in s1:
    if c == prev:
        nwrd += 1
    else:
        if nwrd > nmax:
            nmax = nwrd
            cmax = prev
        prev = c
        nwrd = 1

print '%s%i' % (cmax, nmax)

clast = ''
chash = {}
for c in s1:
    if c == clast:
        nlist = chash[c]
        nlist[-1] += 1
    else:
        clast = c
        try:
            chash[c].append(1)
        except KeyError:
            chash[c] = [1]

lst = sorted(list((max(nlist), c) for c, nlist in chash.items()), reverse=True)
print '%s%i' % lst[0][::-1]