Python (improved) Math Quiz App (with datetime), formatting within a try: except block with ValueError

# user defined # of questions?
# user defined range for questions?
# time to asnwer each question?

import datetime
import random

from questions import Add, Multiply

# user input for number of questions
while True:
        try:
            num_of_questions = int(input("How many questions would you like? (Integers only) > "))
            break 
        except ValueError:
            print("Hey smart guy, that ain't no integer I ever heard of!")   

class Quiz:
    questions = []
    answers = []

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


    def take_quiz(self):
        # log start time
        self.start_time = datetime.datetime.now()

        # ask questions
        for question in self.questions:
            # log if questions asnwered correctly
            self.answers.append(self.ask(question))
        else:
            # log the end time
            self.end_time = datetime.datetime.now()


        # show a summary
        return self.summary()

    def ask(self, question):
        correct = False
    # log start time
        question_start = datetime.datetime.now()

    # capture answer
        answer = input(question.text + ' ? ')
    # check answer
        if answer == str(question.answer):
            correct = True
    # log end time
        question_end = datetime.datetime.now()
    # if the answer correct, return true, 
    # otherwise send back false
    # return elapsed time
        return correct, question_end - question_start

    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("You got {} out of {} correct!".format(
                self.total_correct(), len(self.questions)
        ))

        if self.total_correct() == len(self.questions):
            print("You must be some kind of genius, you got 'em all right!")

        elif self.total_correct() == 0:
            print("You are a total retard! You answered zero questions correctly!") 

        print("It took you {} seconds total!".format(
                (self.end_time-self.start_time).seconds
        ))

Quiz().take_quiz()

while True:
        try:
            num_of_questions = int(input("How many questions would you like? (Integers only) > "))
            break 
        except ValueError:
            print("Hey smart guy, {} ain't no integer I ever heard of!".format(num_of_questions))  

while True:
        try:
            num_of_questions = int(input("How many questions would you like? (Integers only) > "))
            break 
        except ValueError:
            print("Hey smart guy, {} ain't no integer I ever heard of!".format(ValueError))