Question

我从初学者书中学习python。下面是一本游戏的书籍（绝对初学者的Python编程，第3版）的代码摘录。我的问题很简单。 update（）方法似乎永远不会被调用，但仍然起作用。这是如何运作的？我已经粘贴了整个代码块，所以没有遗漏任何内容。

# Pizza Panic
# Player must catch falling pizzas before they hit the ground

from livewires import games, color
import random

games.init(screen_width = 640, screen_height = 480, fps = 50)


class Pan(games.Sprite):
    """
    A pan controlled by player to catch falling pizzas.
    """
    image = games.load_image("pan.bmp")

    def __init__(self):
        """ Initialize Pan object and create Text object for score. """
        super(Pan, self).__init__(image = Pan.image,
                                  x = games.mouse.x,
                                  bottom = games.screen.height)

        self.score = games.Text(value = 0, size = 25, color = color.black,
                                top = 5, right = games.screen.width - 10)
        games.screen.add(self.score)

    def update(self):
        """ Move to mouse x position. """
        self.x = games.mouse.x

        if self.left < 0:
            self.left = 0

        if self.right > games.screen.width:
            self.right = games.screen.width

        self.check_catch()

    def check_catch(self):
        """ Check if catch pizzas. """
        for pizza in self.overlapping_sprites:
            self.score.value += 10
            self.score.right = games.screen.width - 10 
            pizza.handle_caught()


class Pizza(games.Sprite):
    """
    A pizza which falls to the ground.
    """ 
    image = games.load_image("pizza.bmp")
    speed = 1   

    def __init__(self, x, y = 90):
        """ Initialize a Pizza object. """
        super(Pizza, self).__init__(image = Pizza.image,
                                    x = x, y = y,
                                    dy = Pizza.speed)

    def update(self):
        """ Check if bottom edge has reached screen bottom. """
        if self.bottom > games.screen.height:
            self.end_game()
            self.destroy()

    def handle_caught(self):
        """ Destroy self if caught. """
        self.destroy()

    def end_game(self):
        """ End the game. """
        end_message = games.Message(value = "Game Over",
                                    size = 90,
                                    color = color.red,
                                    x = games.screen.width/2,
                                    y = games.screen.height/2,
                                    lifetime = 5 * games.screen.fps,
                                    after_death = games.screen.quit)
        games.screen.add(end_message)


class Chef(games.Sprite):
    """
    A chef which moves left and right, dropping pizzas.
    """
    image = games.load_image("chef.bmp")

    def __init__(self, y = 55, speed = 2, odds_change = 200):
        """ Initialize the Chef object. """
        super(Chef, self).__init__(image = Chef.image,
                                   x = games.screen.width / 2,
                                   y = y,
                                   dx = speed)

        self.odds_change = odds_change
        self.time_til_drop = 0

    def update(self):
        """ Determine if direction needs to be reversed. """
        if self.left < 0 or self.right > games.screen.width:
            self.dx = -self.dx
        elif random.randrange(self.odds_change) == 0:
           self.dx = -self.dx

        self.check_drop()


    def check_drop(self):
        """ Decrease countdown or drop pizza and reset countdown. """
        if self.time_til_drop > 0:
            self.time_til_drop -= 1
        else:
            new_pizza = Pizza(x = self.x)
            games.screen.add(new_pizza)

            # set buffer to approx 30% of pizza height, regardless of pizza speed   
            self.time_til_drop = int(new_pizza.height * 1.3 / Pizza.speed) + 1      


def main():
    """ Play the game. """
    wall_image = games.load_image("wall.jpg", transparent = False)
    games.screen.background = wall_image

    the_chef = Chef()
    games.screen.add(the_chef)

    the_pan = Pan()
    games.screen.add(the_pan)

    games.mouse.is_visible = False

    games.screen.event_grab = True
    games.screen.mainloop()

# start it up!
main()

Answer 1

每个对象的update（）方法由您在顶部导入的游戏模块调用：

from livewires import games, color

这些模块正在处理的GUI在一个管理事件和回调的循环中运行。

如果您感到好奇，可以打开加载并阅读这些文件，并了解代码的工作原理。你会发现每个对象反过来调用它自己的update（）方法。

Answer 2

您正在使用已在顶部导入的框架 livewires。该框架将使用objects，然后调用它们上的方法，而不是调用方法。

有关框架和库之间差异的高级视图，请参阅此页面：Framework vs. Toolkit vs. Library

在python中调用方法

2 个答案: