可以在 中对人体桨进行“屏幕外检查” control_human。如果桨向上移动，则最终桨顶部位置是max0 和 中的最大值 ( ) paddle.rect.top-5。如果桨向下移动，则最终桨底部位置是和 中min的最小值 ( ) ：SCREEN_HEIGHT``paddle.rect.bottom+5

def control_human(paddle):
    keys_pressed = pygame.key.get_pressed()
    if keys_pressed[pygame.K_UP]:
        paddle.rect.top = max(0, paddle.rect.top - 5)
    if keys_pressed[pygame.K_DOWN]:
        paddle.rect.bottom = min(SCREEN_HEIGHT, paddle.rect.bottom + 5)

要计算分数，请向函数添加返回值。如果球与挡板相撞，则check_collision函数必须返回。否则，函数返回：True``False

def check_collision(ball, paddle):
    if ball.rect.colliderect(paddle.rect):
        ball.dx *= -1
        return True
    return False

如果与发生碰撞，则添加score并增加分数。将分数转换为字符串，渲染字符串并将其 blit 到显示器上： left_paddle``ballstr

score = 0
while True:
    # [...]

    if not ball.game_over:
        ball.move()
        ball.draw(screen)
        control_human(left_paddle)
        control_computer(right_paddle, ball)
        left_paddle.draw(screen)
        right_paddle.draw(screen)

        if check_collision(ball, left_paddle):
            score += 1

        check_collision(ball, right_paddle)

        score_label = font.render(str(score), 1, (255, 0, 0, 255))
        screen.blit(score_label, (10, 10))

    else:
        screen.blit(label, (50, 100) )

    # [...]

完整示例：

import pygame

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600

WHITE = (255, 255, 255)
BLACK = (0, 0, 0)

class Ball:
    # свойства
    def __init__(self):
        self.rect = pygame.Rect(0, 0, 20, 20)
        self.rect.center = (SCREEN_WIDTH // 2, SCREEN_HEIGHT // 2)
        self.dx = 5     # скорость по иксу
        self.dy = 5     # скорость по игреку
        self.game_over = False

    # методы
    def draw(self, screen):
        pygame.draw.circle(screen, WHITE, self.rect.center, 10)     # 10 - радиус мяча

    def move(self):
        x, y = self.rect.center
        x += self.dx
        y += self.dy
        self.rect.center = (x, y)
        if y > SCREEN_HEIGHT or y < 0:
            self.dy *= -1
        if x > SCREEN_WIDTH or x < 0:
            #self.dx *= -1
            print('Game Over')
            self.game_over = True          

class Paddle:   # ракетка
    def __init__(self, x, y):
        self.rect = pygame.Rect(x, y, 10, 100)

    def draw(self, screen):
        pygame.draw.rect(screen, WHITE, self.rect)

# ----------------  проверка на столкновение -------------------------- #

def check_collision(ball, paddle):
    if ball.rect.colliderect(paddle.rect):
        ball.dx *= -1
        return True
    return False

# -------------------- управление ракетками --------------------------- #

def control_human(paddle):
    keys_pressed = pygame.key.get_pressed()
    if keys_pressed[pygame.K_UP]:
        paddle.rect.top = max(0, paddle.rect.top - 5)
    if keys_pressed[pygame.K_DOWN]:
        paddle.rect.bottom = min(SCREEN_HEIGHT, paddle.rect.bottom + 5)

def control_computer(paddle, ball):
    # если мяч летит от компьютера, то ничего не делать
    if ball.dx < 0:
        return
    # если мяч выше ракетки, то двигаем ракетку вверх
    if ball.rect.y < paddle.rect.y:
        paddle.rect.y -= 5
        if paddle.rect.y < 0:
            paddle.rect.y = 0
    # если мяч ниже ракетки, то двигаем ракетку вниз
    if ball.rect.y > paddle.rect.y:
        paddle.rect.y += 5
        #if paddle.rect.y + 100 > SCREEN_HEIGHT:
        #    paddle.rect.y = SCREEN_HEIGHT - 100
        if paddle.rect.bottom > SCREEN_HEIGHT:
            paddle.rect.bottom = SCREEN_HEIGHT    

# --------------------------------------------------------------------- #
pygame.init()
screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))

# ----------------  создаем объекты для игры -------------------------- #

ball = Ball()
left_paddle = Paddle(30, SCREEN_HEIGHT // 2 - 50)
right_paddle = Paddle(SCREEN_WIDTH - 40, SCREEN_HEIGHT // 2 - 50)
clock = pygame.time.Clock()
font = pygame.font.SysFont("Lucida Console", 30)
label = font.render("G A M E   O V E R", 1, (255, 0, 0, 255))

# --------------------  главный цикл игры ----------------------------- #
score = 0
while True:
    screen.fill(BLACK)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()

    if not ball.game_over:
        ball.move()
        ball.draw(screen)
        control_human(left_paddle)
        control_computer(right_paddle, ball)
        left_paddle.draw(screen)
        right_paddle.draw(screen)
        if check_collision(ball, left_paddle):
            score += 1
            print(score)
        check_collision(ball, right_paddle)
        score_label = font.render(str(score), 1, (255, 0, 0, 255))
        screen.blit(score_label, (10, 10))
    else:
        screen.blit(label, (50, 100) )

    pygame.display.update()
    clock.tick(60)