Python-сообщество

f = open('input.txt','r')
dict = {}
for line in f.readlines():
    if line[-1:] == '\n': l = line[:-1]
    else: l = line
    if l in dict: dict[l] += 1
    else: dict[l] = 1
f.close()
f = open('output.txt','w')
for item in sorted(dict, key=lambda x: int(dict[x]), reverse=True):
    f.write(item+' '+str(dict[item])+'\n')
f.close()

#!/usr/bin/env python
#coding: utf8

import sys
from collections import Counter

TEST_DATA='''test0
test0
test0
test1
test2
test2
'''.splitlines()

def process_data(iterable):
    cnt = Counter()
    for item in iterable:
        cnt[item]+=1
    return cnt

def read_file(name):
    with open(name) as fd:
        lines = filter(bool,\
                       map(lambda a: a.strip(), fd))
    return lines

def main(args):
    data = read_file(args[1]) if len(args) == 2 \
                              else TEST_DATA
    stat = process_data(data)

    print '\n'.join(map(lambda a: '%d: %s' % (a[1], a[0]),\
                        sorted(stat.items(), key=lambda a: a[1], reverse=True)))
    return 0

sys.exit(main(sys.argv))

from collections import Counter
l=[i.strip() for i in open("a.dat")]
print Counter(l).most_common(len(l))