#!/usr/bin/env python
 
from operator import add, sub
from random import randint, choice
 
ops = {'+': add, '-':sub}
#定义一个字典
MAXTRIES = 2
 
def doprob():
    op = choice('+-')
    #用choice从'+-'中随意选择操作符
    nums = [randint(1,10) for i in range(2)]
    #用randint(1,10)随机生成一个1到10的数,随机两次使用range(2)
    nums.sort(reverse=True)
    #按升序排序
    ans = ops[op](*nums)
    #利用函数
    pr = '%d %s %d = ' % (nums[0], op, nums[1])
    oops = 0
    #oops用来计算failure测试,当三次时自动给出答案
    while True:
        try:
            if int(raw_input(pr)) == ans:
                print 'correct'
                break
            if oops == MAXTRIES:
                print 'answer\n %s%d' % (pr, ans)
                break
            else:
                print 'incorrect... try again'
                oops += 1
        except (KeyboardInterrupt, EOFError, ValueError):
            print 'invalid ipnut... try again'
def main():
    while True:
        doprob()
        try:
            opt = raw_input('Again? [y]').lower()
            if opt and opt[0] == 'n':
                break
        except (KeyboardInterrupt, EOFError):
            break
 
if __name__ == '__main__':
    main()