What is wrong with this Bagels program?

Im a beginner programer and i need some help with the following: I have written a Bagels program and it isnt working: I have no idea how to fix it. Please can someone help me!!! It keeps on saying the secretnumber is not defined, and i defined it near the beginning of name: Its based on some code(I didnt actually look at the code, just the example run, as i wanted a challenge)from Invent your own computer game 2nd edition. This is the program:

import random

def secretnum():
    numbers = list('0123456789')
    random.shuffle(numbers)
    secretnumber = ''
    numdigits = 3
    for  i in range(numdigits):
        secretnumber += str(numbers[i])
    return secretnumber

def ask():
    print("Do you want to play again?(y/n): ")
    ans = input()
    if ans == "y":
        print("Ok then!")
        main()
    elif ans == "n":
        print("OOF")
        exit()
    else:
        print("...Invalid...")
        ask()

def getclues(guess, secretnumb):
    if guess == secretnumber:
        return 'You ot it!!!'
    clues = []

    for i in range(len(guess)):
        if guess[i] == secretnumber[i]:
            clues.append('Fermi')
        elif guess[i] in secretnumber:
            clues.append('Pico')
    if len(clues) == 0:
        return 'Bagels'
    else:
        clues.sort()
        return ''.join(clues)
    if __name__ == '__main__':
        main()

def main():
    print('''
    Im thinking of a three digit number. Try to guess what it is.")
    Here are some clues:
    When I say:             That means:
    Pico                    One digit is correct and in the wrong place
    Fermi                   One digit is correct and in the right position
    Bagels                  No digit is correct.
    ''')

    maxguesses = 20

    secretnumber = secretnum()
    print('I have a number.')
    print('You have to guess it!'.format(maxguesses))

    numGuesses = 1
    while numGuesses <= maxguesses:
        guess = ''
        print('Guess #{}: '.format(numGuesses))
        guess = input('> ')

        clues = getclues(guess, secretnumber)
        print(clues)
        numGuesses += 1
        if guess == secretnumber:
            print("You got it!!!")
            ask()
        if numGuesses > maxguesses:
            print('You ran out of guesses.')
            print('The answer was {}.'.format(secretnumber))
            ask()

main()