Python计算时间差

import datetime
import time

oldtime=datetime.datetime.now()
print oldtime;
time.sleep(1)
newtime=datetime.datetime.now()
print newtime;
print '相差：%s'%(newtime-oldtime)
print '相差：%s微秒'%(newtime-oldtime).microseconds
print '相差：%s秒'%(newtime-oldtime).seconds