In Better with Set(ter) the code Kenneth uses in the video is different from the one he made back in python basics.

import os
import random
import sys

# make a list of words
words = [
    'colt',
    'filly',
    'foal',
    'mare',
    'horse',
    'stallion',
    'martingale',
    'saddle',
    'gelding',
    'bale',
    'flake',
    'bit',
    'reins',
]

def clear():
    if os.name == 'nt':
        os.system('cls')
    else:
        os.system('clear')

def draw(bad_guesses, good_guesses, secret_word):
    clear()

    print('Strikes: {}/7'.format(len(bad_guesses)))
    print('')

    for letter in bad_guesses:
        print(letter, end='')
    print('\n\n')

    # draw guessed letters, spaces, and strikes
    for letter in secret_word:
        if letter in good_guesses:
            print (letter, end='')
        else:
            print ('_', end='')

    print('')

def get_guess(guess):
    while True:
        # take guess
        guess = input ("Guess a letter: ").lower()

        # print ot win/lose
        if len(guess) != 1:
            print ("You can only guess a single letter!")

        elif guess in bad_guesses or guess in good_guesses:
            print ("You've already guessed that letter!")

        elif not guess.isalpha():
            print ("You can only guess letters!")

        else:
            return guess


def play(done):
    clear()
    secret_word = random.choice(words)
    bad_guesses = set()
    good_guesses = set()
    word_set = set(secret_word)

    while True:
        draw (bad_guesses, good_guesses, secret_word)
        guess = get_guess(bad_guesses | good_guesses)

        if guess in word_set:
            good_guesses.add(guess)
            if not word_set.symmetric_difference(good_guesses):
                print("You win!")
                print("The secret word was {}.".format(secret_word))
                done = True
        else:
            bad_guesses.add(guess)
            if len(bad_guesses) == 7:
                draw(bad_guesses, good_guesses, secret_word)
                print("You lost! Time next luck better. :)")
                print("The secret word was {}.".format(secret_word))
                done = True

        if done:
            play_again = input("Play again? Y/n: ").lower()
            if play_again != 'n':
                return play(done=False)
            else:
                sys.exit()


def welcome():
    print('Welcome to Letter Guess!')

    start = input("Press enter/return to start or Q to quit: ").lower()
    if start == 'q':
        print("Bye!")
        sys.exit()
    else:
        return True

done = False

while True:
    clear()
    welcome()
    play(done)