Python: Get time delta from log with YYYY-MM-DD hh:mm:ss format

gistfile1.txt

#!/usr/bin/env python

import sys
from datetime import datetime
from argparse import ArgumentParser

parser = ArgumentParser()
parser.add_argument('logfile', help='Log file')
parser.add_argument('-s', '--seconds', default=1, type=int,
        help='Only log entries that took over n seconds')
args = parser.parse_args()

with open(args.logfile, 'r') as logf:
    log = logf.readlines()

lasttime = None
for line in log:
    datestr, timestr = line.split()[0], line.split()[1]
    datetimestr = '{} {}'.format(datestr, timestr)
    timeobj = datetime.strptime(datetimestr, '%Y-%m-%d %H:%M:%S')
    if lasttime:
        delta = timeobj - lasttime
        if delta.seconds > args.seconds:
            print '{}s {}'.format(delta.seconds, lastline)
    lasttime = timeobj
    lastline = line.strip()