title: Str object has no attribute "add"
body: <p>Can someone help me fix this:</p>
  
  <pre><code>import random
  import operator
  from operator import add, sub, mul
  from random import randint
  
  score = 0
  
  name = input("What is your name? ")
  
  for i in range(10):
      n1 = randint(1,10)
      n2 = randint(1,10)
      ops =[["+", operator.add],["-", operator.sub],["*", operator.mul]]
  
      randomOp = random.choice(list(ops))
  
      operator = randomOp[0]
      op = randomOp[1]
  
      prod = op(int(n1), int(n2))
  
      ask = ("What is",int(n1),operator,int(n2),"?")
  
      ans = input(ask)
      if ans == ("%d" % (prod)):
          print ("That's right -- well done")
          score = score + 1
      else:
          print ("No, The answer is %d. " % (prod))
  
  print (name, "I asked you 10 questions. You got %d of them right." % (score))
  print ("Quiz is finished")
  </code></pre>