如何从另一个对象的对象引用变量？

如果要访问对象的属性，则需要引用该对象的变量。

我建议使用工具2个单独的类Ball和Location。位置类不需要步骤属性，也不需要move方法。

class Location:
    def __init__(self, x, y, x_step, y_step, color, radius, screen):
        self.x = x
        self.y = y
        self.x_step = x_step
        self.y_step = y_step
        self.color = color
        self.radius = radius
        self.screen = screen
    def move(self):
        self.x += self.x_step
        self.y += self.y_step

        if not self.radius <= self.x <= SCREEN_WIDTH - self.radius:
            self.x_step = 0
            self.y_step = 0
            
        if not self.radius <= self.y <= SCREEN_HEIGHT - self.radius:
            self.y_step = 0
            self.x_step = 0
    def draw(self):
        pygame.draw.circle(self.screen, self.color, (self.x, self.y), self.radius, 2)

获取新参数的move方法Ball``。每次球反弹时，Location都会附加一个新对象：

class Ball:
    def __init__(self, x, y, x_step, y_step, color, radius, screen):
        self.x = x
        self.y = y
        self.x_step = x_step
        self.y_step = y_step
        self.color = color
        self.radius = radius
        self.screen = screen
    def move(self, bounce_locations):
        self.x += self.x_step
        self.y += self.y_step

        if not self.radius <= self.x <= SCREEN_WIDTH - self.radius:
           self.x_step *= -1
           bounce_locations.append(Location(self.x, self.y, self.color, self.radius, self.screen))

        if not self.radius <= self.y <= SCREEN_HEIGHT - self.radius:
            self.y_step *= -1
            bounce_locations.append(Location(self.x, self.y, self.color, self.radius, self.screen))

    def draw(self):
        pygame.draw.circle(self.screen, self.color, (self.x, self.y), self.radius)

完整的例子：

import pygame
import random

WHITE = (255, 255, 255)
BLACK = (0, 0, 0)
RED = (255, 0, 0)
GREEN = (0, 255, 0)
BLUE = (0, 0, 255)

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600

MAX_RADIUS = 30
NUMBER_OF_BALLS = 1

class Location:
    def __init__(self, x, y, color, radius, screen):
        self.x = x
        self.y = y
        self.color = color
        self.radius = radius
        self.screen = screen
    def draw(self):
        pygame.draw.circle(self.screen, self.color, (self.x, self.y), self.radius, 2)

class Ball:
    def __init__(self, x, y, x_step, y_step, color, radius, screen):
        self.x = x
        self.y = y
        self.x_step = x_step
        self.y_step = y_step
        self.color = color
        self.radius = radius
        self.screen = screen
    def move(self, bounce_locations):
        self.x += self.x_step
        self.y += self.y_step

        if not self.radius <= self.x <= SCREEN_WIDTH - self.radius:
           self.x_step *= -1
           bounce_locations.append(Location(self.x, self.y, self.color, self.radius, self.screen))

        if not self.radius <= self.y <= SCREEN_HEIGHT - self.radius:
            self.y_step *= -1
            bounce_locations.append(Location(self.x, self.y, self.color, self.radius, self.screen))

    def draw(self):
        pygame.draw.circle(self.screen, self.color, (self.x, self.y), self.radius)

def main():
    pygame.init()
    screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))

    colors = [WHITE, RED, GREEN, BLUE]
    balls = []
    bounce_locations = []
    for _ in range(NUMBER_OF_BALLS):
        x = random.randrange(MAX_RADIUS, SCREEN_WIDTH - MAX_RADIUS)
        y = random.randrange(MAX_RADIUS, SCREEN_HEIGHT - MAX_RADIUS)
        x_step = random.choice([-3, -2, -1, 1, 2, 3])
        y_step = random.choice([-3, -2, -1, 1, 2, 3])
        color = random.choice(colors)
        radius = random.randrange(5, MAX_RADIUS)
        moving_ball = Ball(x, y, x_step, y_step, color, radius, screen)
        balls.append(moving_ball)

    running = True
    clock = pygame.time.Clock()
    while running:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                running = False
        
        for ball in balls:
            ball.move(bounce_locations)
        
        screen.fill(BLACK)
        for ball in balls:
            ball.draw()
        for location in bounce_locations:
            location.draw()

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


if __name__ == "__main__":
    main()