#! /usr/bin/env python

from operator import add, sub
from random import randint, choice

ops = {'+': add, '-': sub}
MAXTRIES = 2

def doprob():
    op = choice('+-')
    nums = [randint(1,10) for i in range(2)]
    nums.sort(reverse=True)
    ans = ops[op](*nums)
    pr = '%d %s %d = ' % (nums[0], op, nums[1])
    oops = 0
    while True:
        try:
            if int(raw_input(pr)) == ans:
                print 'correct'
                break
            if oops == MAXTRIES:
                print 'answer\n%s%d' % (pr, ans)
            else:
                print 'incorrect... try again'
                oops += 1
        except (KeyboardInterrupt, EOFError, ValueError):
            print 'invalid input... 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()

6 + 2 = 1
incorrect... try again
6 + 2 = 1
incorrect... try again
6 + 2 = 1
answer
6 + 2 = 8
6 + 2 = 1
answer
6 + 2 = 8
6 + 2 = 8
correct
Again? [y] y
10 + 7 = 17
correct
Again? [y] y
10 - 5 = 0
incorrect... try again
10 - 5 = 0
incorrect... try again
10 - 5 = 0
answer
10 - 5 = 5
10 - 5 = 5
correct
Again? [y] n