车羊门问题

之前一直在准备比赛的事，今天把代码贴上来。

import time
import random
change_time = 0
no_change_time = 0
car = 0
select = 0
try:
    f = eval(input("输入羊车门问题测试次数："))
    start = time.clock()
    for i in range(1,f+1):
        car = random.randint(1,3)
        select = random.randint(1,3)
        if car==select:
            no_change_time = no_change_time+1
        else:
            change_time = change_time+1
    print("不改变得车概率{}".format(no_change_time/f))
    print("改变后得车概率{}".format(change_time/f))
    end = time.clock()
    print("运行时间: %f s" % (end - start))
except:
    print("发生错误！请输入一个整数！")