Problem with quiz.py for the Quiz class video. I keep getting quiz_types is not defined.

def __init__(self):
self.question_types = (Add, Multiply)
    # generate 10 random questions with numbers from 1 to 10
for _ in range(10):
    num1 = random.randint(1, 10)
    num2 = random.randint(1, 10)
    question = random.choice(question_types)(num1, num2)
        # add these questions into self.questions
    self.questions.append(questions)


def take_quiz(self):
    # log the start time
    # ask all of the questions
    # log if they got the question right
    # log the end time
    # show a summary
    pass

def ask(self, question):
    # log the start time
    # capture the answer
    # check the answer
    # log the end time
    # if the answer's right, send back True
    # otherwise, send back False
    # send back the elapsed time, too
    pass

def total_correct(self):
    # return the total # of correct answers
    total = 0
    for answer in self.answers:
        if answer[0]:
            total += 1
    return total


def summary(self):
    # print how many you got right and the total # of questions. 5/10
    print("You got {} out of {} right.".format(
            self.total_correct(), len(self.questions)
    ))
    # print the total time for the quiz: 30 seconds!
    print("It took you {} seconds total".format(
            (self.end_time-self.start_time).seconds
    ))