If Statement Issues User InPut

import random
import string

def consonant_count(word):
    word = word.lower()
    return len([x for x in word if x in consonants])

def vowel_count(word):
    word = word.lower()
    return len([x for x in word if x in vowels])

def prompt_letter_count(word):
    correct = word_map[word]['letters']
    ans = input('How many letters does "{}" contain?'.format(word))
    if ans.isalpha():
        print('Please type in numbers')
    else:
        return check(int(ans), correct)

def prompt_vowel_count(word):
    correct = word_map[word]['vowels']
    ans = input('How many vowels does "{}" contain?'.format(word))
    if ans.isalpha():
        print('Please type in numbers')
    else:
        return check(int(ans), correct)

def prompt_consonant_count(word):
    correct = word_map[word]['consonants']
    ans = input('How many consonants does "{}" contain?'.format(word))
    if ans.isalpha():
        print('Please type in numbers')
    else:
        return check(int(ans), correct)

def prompt_random_letter(word):
    n = random.randint(1, len(word))
    correct = word[n-1]
    ans = input('What is letter {} of "{}"?'.format(n, word))
    return check(ans.lower(), correct.lower())

def check(ans, correct):
    if ans == correct:
        return prompt_correct()
    return prompt_incorrect()


def prompt_correct():
    print('That is correct! :)')
    return 1

def prompt_incorrect():
    print('That is incorrect :(')
    return 0

def next_question(word):
    q_type = input_map[random.randint(1, 4)]
    return q_type(word)

vowels = ['a', 'e', 'i', 'o', 'u']
consonants = [x for x in string.ascii_lowercase if x not in vowels]
quizWords = ['WOMBAT', 'COMPUTER', 'BOOKS', 'DAY', 'NIGHT', 'HOUR', 'POTATO', 'HUGE', 'TINY', 'GOOD', 'BAD', 'YES', 'NO', 'HOUSE', 'QUESTION', 'BALLOON', 'CAT', 'DUCK', 'KOOKARBURRA', 'POSTER', 'TELEVISION', 'PRINCE', 'RHYTHM', 'SUDDENLY', 'SNOW', 'MAGNET', 'TOWEL', 'WALKING', 'SPEAKER', 'UNCHARACTERISTICALLY']
word_map = {x:{'consonants':consonant_count(x), 'vowels':vowel_count(x), 'letters':len(x)} for x in quizWords}
input_map = {1:prompt_letter_count, 2:prompt_vowel_count, 3:prompt_consonant_count, 4:prompt_random_letter}

def start_quiz(number_questions):
    current_question = 0
    correct_questions = 0
    if number_questions > len(quizWords):
        number_questions = len(quizWords)
    sample_questions = random.sample(quizWords, number_questions)
    print('WELCOME TO YOUR QUIZ')
    print ('---------------------')
    for x in sample_questions:
        print ("Question {}/{}:".format(current_question+1, number_questions))
        correct_questions += next_question(x)
        print ('---------------------')
        current_question += 1
    print ('Congragulations on completing your quiz!')
    print ("    Score {}/{}:".format(correct_questions , number_questions))
    try_again = input('Would you like to try again? (y/n)').lower()
    if try_again == 'y' or try_again == 'yes':
        start_quiz(number_questions)

start_quiz(5)

Trying to add some validation to a quiz app application for year 1 english students. I'm trying to get the questions to not allow letters in questions that ask for a number or amount and vice versa for questions such as "what the nth letter to not allow digits to be entered"

From what I can see from the the if statement should work but when I test it I get. How am I screwing this up what am I doing wrong here?

WELCOME TO YOUR QUIZ

---

Question 1/5:

How many vowels does "POTATO" contain?a

Please type in numbers

Traceback (most recent call last): File "C:\Users\Mike\Desktop\MYQUIZ\MY QUIZ.py", line 85, in start_quiz(5)

File "C:\Users\Mike\Desktop\MYQUIZ\MY QUIZ.py", line 76, in start_quiz correct_questions += next_question(x) TypeError: unsupported operand type(s) for +=: 'int' and 'NoneType'