Interactive Integer problem generator for kids

int_prob_gen.py

import random

def pm(x):
    if x>0:
        return "+"
    else:
        return ""
    
def int_prob_gen(n):
    s=0
    for i in xrange(n):
        x=random.randrange(-10,11)
        y=random.randrange(-10,11)
        op=["+","-"][random.randrange(2)]
        eval_string="({0}){1}({2})".format(x,op,y)
        right_ans=eval(eval_string)
        parse_correct=False
        while parse_correct==False:
            answer_string= raw_input("({0}{1}){2}({3}{4}) = ".format(pm(x),x,op,pm(y),y))
            answer=123232324
            try:
                answer=int(answer_string)
            except:
                print "Invalid Input! Please try again"
                continue
            parse_correct=True
            if answer==right_ans:
                s+=1
                print ["Nice going!","Good Job","You are doing Great","Fantastic","You Rock!"][random.randrange(5)]
            else:
                print "The correct answer was {0}, but you entered {1}.\nBetter luck next time!".format(right_ans,answer)
    print "You got {0} out of {1} correct!".format(s,n)