wacky

import sys
from itertools import islice


def window(seq, n=2):
    "Returns a sliding window (of width n) over data from the iterable"
    "   s -> (s0,s1,...s[n-1]), (s1,s2,...,sn), ...                   "
    it = iter(seq)
    result = tuple(islice(it, n))
    if len(result) == n:
        yield result
    for elem in it:
        result = result[1:] + (elem,)
        yield result

f = open(sys.argv[1], 'r')

lines = f.readlines()

for (i, (prev2, prev1, line)) in enumerate(window(lines, 3)):
    if len(line) > (100 * 1000):
        print "PREV2: %s" % prev2.strip()
        print "PREV1: %s" % prev1.strip()
        print "LINE: #: %d length: %d start: %s end: %s" % \
              (i, len(line), line[22:100], line[-40:])
        print ""