Pygame part 2

import pygame

pygame.init()
screen = pygame.display.set_mode((900, 500))
pygame.display.set_caption('My game')
clock = pygame.time.Clock()
player = pygame.rect.Rect(10, 200, 20, 100)
bot = pygame.rect.Rect(870, 200, 20, 100)
ball = pygame.rect.Rect(445, 245, 10, 10)
running = True
player_speed_y = 0
ball_speed_x = -2
ball_speed_y = 2


def move_bot():
    if ball.centery > bot.centery and ball.centerx>450:
        bot.y += 1
    if ball.centery < bot.centery and ball.centerx>450:
        bot.y -= 1


def ball_check():
    global ball_speed_y
    global ball_speed_x
    if ball.top <= 0:
        ball_speed_y = -ball_speed_y
    if ball.bottom >= 500:
        ball_speed_y = - ball_speed_y
    if ball.colliderect(bot) or ball.colliderect(player):
        ball_speed_x = -ball_speed_x


while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_UP:
                player_speed_y -= 1
            if event.key == pygame.K_DOWN:
                player_speed_y += 1

        if event.type == pygame.KEYUP:
            if event.key == pygame.K_UP:
                player_speed_y += 1
            if event.key == pygame.K_DOWN:
                player_speed_y -= 1

    player.y += player_speed_y
    ball.x += ball_speed_x
    ball.y += ball_speed_y
    ball_check()
    move_bot()
    screen.fill((0, 0, 0))
    pygame.draw.rect(screen, (20, 200, 20), player)
    pygame.draw.rect(screen, (200, 20, 20), bot)
    pygame.draw.ellipse(screen, (255, 255, 255), ball)
    pygame.display.flip()
    clock.tick(60)