aspath.py

from collections import Counter

FILENAME = 'aspath.txt'

f = open(FILENAME, 'r')

for line in f:
    # print 'Line read is ', line
    mylist = line.split()
    
    # Coalesce adjacent identical values.
    newlist = list()
    
    if len(mylist) > 0:
        i = 1
        newlist.append(mylist[0])
        while i < len(mylist):
            if mylist[i - 1] != mylist[i]:
                newlist.append(mylist[i])
            i += 1
    
    result = [k for k, v in Counter(newlist).items() if v > 1]
    if result :
        print '%s -> %s' % (line.strip(), result)