How to Detect User Idle Time or Inactivity in Acess logs

How to Detect User Idle Time or Inactivity in Acess logs
Requirement:

• Read access log
• Find the top most idle time(s) between the requests

Script

import itertools
import datetime
import logging

fo = open("access_log_time", "r+")
print "Name of the file: ", fo.name

lst = fo.readlines()
print len(lst)

def diff_date(x, y):
diff=0
try:
x = x.strip()
y = y.strip()
d1 = datetime.datetime.strptime(x, '%d/%b/%Y:%H:%M:%S')
d2 = datetime.datetime.strptime(y, '%d/%b/%Y:%H:%M:%S')
diff = (d2 - d1).total_seconds()
print '-------'
print diff
print x
print y
except Exception, e:
logging.error(e)
return int(diff)

#zip Vs izip
#zip computes all the list at once, izip computes the elements only when requested.
#One important difference is that 'zip' returns an actual list, 'izip' returns an 'izip #object', which is not a list and does not support list-specific features

res= [diff_date(x,y) for x, y in itertools.izip (lst, lst[1:])]
print sorted(res, reverse=True)
#print res