python计算时间间隔（精确到微妙）

import datetime
oldtime=datetime.datetime.now()
print oldtime;
x=1
while x<10000000:
    x=x+1
newtime=datetime.datetime.now()
print newtime;
print u'相差：%s'%(newtime-oldtime)
print u'相差：%s微秒'%(newtime-oldtime).microseconds
print u'相差：%s秒'%(newtime-oldtime).seconds