GUI Zero emoji game timed

import os
from random import shuffle, randint
from guizero import App, Box, Picture, Text, PushButton, warn

# set the path to the emoji folder on your computer
emojis_dir = "emojis"
# create a list of the locations of the emoji images
emojis = [os.path.join(emojis_dir, f) for f in os.listdir(emojis_dir) if os.path.isfile(os.path.join(emojis_dir, f))]
# shuffle the emojis
shuffle(emojis)

def match_emoji(matched):
    if matched:
        result.value = "Correct"
    else:
        result.value = "Incorrect"
    setup_round()

def setup_round():
    global num_rounds
    emojis = [os.path.join(emojis_dir, f) for f in os.listdir(emojis_dir) if os.path.isfile(os.path.join(emojis_dir, f))]
    shuffle(emojis)

    for picture in pictures:
        picture.image = emojis.pop()

    for button in buttons:
        button.image = emojis.pop()
        button.update_command(match_emoji, [False])

    matched_emoji = emojis.pop()

    random_picture = randint(0,8)
    pictures[random_picture].image = matched_emoji

    random_button = randint(0,8)
    buttons[random_button].image = matched_emoji
    buttons[random_button].update_command(match_emoji, [True])

    num_rounds = num_rounds + 1
    rounds_played.value = "Round " +str(num_rounds)

def counter():
    global num_rounds
    timer.value = int(timer.value) - 1
    if int(timer.value) == 0:
        timer.cancel(counter)
        result.value = "Game Over"
        warn("Time Up", "You have run out of time!")
        timer.value = 20
        result.value = ""
        setup_round()
        timer.repeat(1000, counter)
        num_rounds = 0

num_rounds = 0

app = App("Emoji Match")
result = Text(app)
rounds_played = Text(app, text="Round " + str(num_rounds))

game_box = Box(app, layout="grid")

# create a box to house the grid
pictures_box = Box(game_box, layout="grid", grid=[0,0])
buttons_box = Box(game_box, layout="grid", grid =[1,0])
# create an empty list to which pictures will be added
buttons = []
pictures = []
for x in range(0,3):
    for y in range(0,3):
        # put the pictures into the list
        picture = Picture(pictures_box, grid=[x,y])
        pictures.append(picture)

        button = PushButton(buttons_box, grid=[x,y])
        buttons.append(button)

extra_features = Box(app)
timer = Text(extra_features, text="Get Ready")

setup_round()

timer.value = 20
timer.repeat(1000, counter)

app.display()