试图了解使用对象和类的简单python游戏的流程和逻辑

我正在通过Learn Python the Hard Way教程.我已经回过头几个练习,试图真正了解Zed的(作者)OOP示例游戏(练习43).

谨慎,我想我明白了 - 什么类和对象是什么.我在理论上至少理解鱼和鲑鱼,汽车和本田等之间的区别.

我知道我们使用类和对象(而不是只按需编写函数)以重用代码(对吧？).

我的思绪链条现在很微妙,但我不能休息,睡觉或感觉满足,直到我真正点击这一点.

游戏中有许多场景(场景是游戏中的一个类).例如中央走廊,大桥,Escape Pod.

除了场景之外,游戏还使用引擎和地图(对象).我完全不了解这些组件如何使游戏运行.

在脚本的最后,开始游戏的是代码块:

a_map = Map('central_corridor')
a_game = Engine(a_map)
a_game.play() 

具体问题:

游戏如何从一个场景移动到另一个场景？

引擎和地图类如何在游戏中运行？即引擎和地图有什么作用？我无法完全遵循逻辑.理想情况下,这可以用一个例子来解释,例如代码中从TheBridge移动到EscapePod的步骤(游戏流程中的最后两个场景)

我的陈述是否正确:"我理解我们使用类和对象(而不是仅按需编写函数)以便重用代码."

这是游戏:

from sys import exit
from random import randint

class Scene(object):
    def enter(self):
        print "This scene is not yet configured. Subclass it and implement enter()."

class Engine(object):

    def __init__(self, scene_map):
        print "Engine __init__ has scene_map", scene_map
        self.scene_map = scene_map

    def play(self):
        current_scene = self.scene_map.opening_scene()
        print "Play's first scene", current_scene

        while True:
            print "\n--------"
            next_scene_name = current_scene.enter()
            print "next scene", next_scene_name
            current_scene = self.scene_map.next_scene(next_scene_name)
            print "map returns new scene", current_scene

class Death(Scene):

    quips = [
        "You died. You kinda suck at this.",
        "Your mom would be proud... if she were smarter",
        "Such a luser",
        "I have a small puppy that's better at this."
        ]

    def enter(self):
        print Death.quips[randint(0, len(self.quips)-1)]
        exit(1)

class CentralCorridor(Scene):

    def enter(self):
        print "The Gothons of Planet Percal #25 have invaded your ship and destroyed"
        print "your entire crew.  You are the last surviving member and your last"
        print "mission is to get the neutron destruct bomb from the Weapons Armory,"
        print "put it in the bridge, and blow the ship up after getting into an "
        print "escape pod."
        print "\n"
        print "You're running down the central corridor to the Weapons Armory when"
        print "a Gothon jumps out, red scaly skin, dark grimy teeth, and evil clown costume"
        print "flowing around his hate filled body.  He's blocking the door to the"
        print "Armory and about to pull a weapon to blast you."

        action = raw_input("> ")

        if action == "shoot!":
            print "Quick on the draw you yank out your blaster and fire it at the Gothon."
            print "His clown costume is flowing and moving around his body, which throws"
            print "off your aim.  Your laser hits his costume but misses him entirely.  This"
            print "completely ruins his brand new costume his mother bought him, which"
            print "makes him fly into an insane rage and blast you repeatedly in the face until"
            print "you are dead.  Then he eats you."
            return 'death'

        elif action == "dodge!":
            print "Like a world class boxer you dodge, weave, slip and slide right"
            print "as the Gothon's blaster cranks a laser past your head."
            print "In the middle of your artful dodge your foot slips and you"
            print "bang your head on the metal wall and pass out."
            print "You wake up shortly after only to die as the Gothon stomps on"
            print "your head and eats you."
            return 'death'

        elif action == "tell a joke":
            print "Lucky for you they made you learn Gothon insults in the academy."
            print "You tell the one Gothon joke you know:"
            print "Lbhe zbgure vf fb sng, jura fur fvgf nebhaq gur ubhfr, fur fvgf nebhaq gur ubhfr."
            print "The Gothon stops, tries not to laugh, then busts out laughing and can't move."
            print "While he's laughing you run up and shoot him square in the head"
            print "putting him down, then jump through the Weapon Armory door."
            return 'laser_weapon_armory'

        else:
            print "DOES NOT COMPUTE!"
            return 'central_corridor'

class LaserWeaponArmory(Scene):

    def enter(self):
        print "You do a dive roll into the Weapon Armory, crouch and scan the room"
        print "for more Gothons that might be hiding.  It's dead quiet, too quiet."
        print "You stand up and run to the far side of the room and find the"
        print "neutron bomb in its container.  There's a keypad lock on the box"
        print "and you need the code to get the bomb out.  If you get the code"
        print "wrong 10 times then the lock closes forever and you can't"
        print "get the bomb.  The code is 3 digits."
        code = "%d%d%d" % (randint(1,9), randint(1,9), randint(1,9))
        guess = raw_input("[keypad]> ")
        guesses = 0

        while guess != code and guesses < 10:
            print "BZZZZEDDD!"
            guesses += 1
            guess = raw_input("[keypad]> ")

        if guess == code:
            print "The container clicks open and the seal breaks, letting gas out."
            print "You grab the neutron bomb and run as fast as you can to the"
            print "bridge where you must place it in the right spot."
            return 'the_bridge'
        else:
            print "The lock buzzes one last time and then you hear a sickening"
            print "melting sound as the mechanism is fused together."
            print "You decide to sit there, and finally the Gothons blow up the"
            print "ship from their ship and you die."
            return 'death'

class TheBridge(Scene):

    def enter(self):
        print "You burst onto the Bridge with the netron destruct bomb"
        print "under your arm and surprise 5 Gothons who are trying to"
        print "take control of the ship.  Each of them has an even uglier"
        print "clown costume than the last.  They haven't pulled their"
        print "weapons out yet, as they see the active bomb under your"
        print "arm and don't want to set it off."

        action = raw_input("> ")

        if action == "throw the bomb":
            print "In a panic you throw the bomb at the group of Gothons"
            print "and make a leap for the door.  Right as you drop it a"
            print "Gothon shoots you right in the back killing you."
            print "As you die you see another Gothon frantically try to disarm"
            print "the bomb. You die knowing they will probably blow up when"
            print "it goes off."
            return 'death'

        elif action == "slowly place the bomb":
            print "You point your blaster at the bomb under your arm"
            print "and the Gothons put their hands up and start to sweat."
            print "You inch backward to the door, open it, and then carefully"
            print "place the bomb on the floor, pointing your blaster at it."
            print "You then jump back through the door, punch the close button"
            print "and blast the lock so the Gothons can't get out."
            print "Now that the bomb is placed you run to the escape pod to"
            print "get off this tin can."
            return 'escape_pod'
        else:
            print "DOES NOT COMPUTE!"
            return "the_bridge"

class EscapePod(Scene):

    def enter(self):
        print "You rush through the ship desperately trying to make it to"
        print "the escape pod before the whole ship explodes.  It seems like"
        print "hardly any Gothons are on the ship, so your run is clear of"
        print "interference.  You get to the chamber with the escape pods, and"
        print "now need to pick one to take.  Some of them could be damaged"
        print "but you don't have time to look.  There's 5 pods, which one"
        print "do you take?"

        good_pod = randint(1,5)
        guess = raw_input("[pod #]> ")


        if int(guess) != good_pod:
            print "You jump into pod %s and hit the eject button." % guess
            print "The pod escapes out into the void of space, then"
            print "implodes as the hull ruptures, crushing your body"
            print "into jam jelly."
            return 'death'
        else:
            print "You jump into pod %s and hit the eject button." % guess
            print "The pod easily slides out into space heading to"
            print "the planet below.  As it flies to the planet, you look"
            print "back and see your ship implode then explode like a"
            print "bright star, taking out the Gothon ship at the same"
            print "time.  You won!"

            return 'finished'

class Map(object):

    scenes = {
        'central_corridor': CentralCorridor(),
        'laser_weapon_armory': LaserWeaponArmory(),
        'the_bridge': TheBridge(),
        'escape_pod': EscapePod(),
        'death': Death()
    }

    def __init__(self, start_scene):
        self.start_scene = start_scene
        print "start_scene in __init__", self.start_scene

    def next_scene(self, scene_name):
        print "start_scene in next_scene"
        val = Map.scenes.get(scene_name)
        print "next_scene returns", val
        return val

    def opening_scene(self):
        return self.next_scene(self.start_scene)

a_map = Map('central_corridor')
a_game = Engine(a_map)
a_game.play()

Anentropic.. 5

游戏的关键部分是这段代码:

while True: 
    next_scene_name = current_scene.enter()  # <-- returns after interaction with user
    current_scene = self.scene_map.next_scene(next_scene_name)

每个场景的enter方法返回要进入的下一个场景的名称(取决于玩家的动作)......这可能是同一个场景.然后该类的next_scene方法Map返回匹配该名称的场景实例,并将其分配给current_scene变量...然后它循环并"进入"新的当前场景.这将无休止地继续,或直到你到达Death退出程序的场景.

Engine上面基本上解释了这个课程.恕我直言,没有必要将它作为一个类,只有一个简单的play函数,如同以下一样有效(并且更简单,因此更好):

def play(scene_map):
    current_scene = scene_map.opening_scene()
    print "Play's first scene", current_scene

    while True:
        print "\n--------"
        next_scene_name = current_scene.enter()
        print "next scene", next_scene_name
        current_scene = scene_map.next_scene(next_scene_name)
        print "map returns new scene", current_scene

并开始运行游戏:

a_map = Map('central_corridor')
play(a_map)

在Map类匹配的场景对象实例场景的名称,如'central_corridor'...之类的核心是包含实际映射的字典.你可以看到next_scene类的方法只get对dict键执行了操作.实际上你可以通过消除Map类来简化代码,只需要一个简单的dict,将简单的起始场景逻辑移动到Engine类中(或者play我上面提到的方法).

然而,在Map类的情况下,我建议通过定义API来提供另一个有用的目的......换句话说,一组与游戏地图相关的方法.这意味着如果你意识到你需要一个更复杂的Map逻辑实现而不仅仅是一个dict,那么在你的游戏开发之后,只要你保持API相同(即方法的名称和参数),你就不要我必须改变你的其余代码.

类定义了一组行为并为它们提供了一个接口.对象是类的实例,它是运行时状态的集合(即类的属性的特定值).

它并不是关于代码重用的.代码重用意味着拥有从父级继承行为的子类(而不是必须复制和粘贴该行为),但是您可以通过使用类来获取值而不进行任何子类化.类就像用于创建具有共同行为的对象的模板.

在目前的游戏代码中,一些类的使用是毫无意义的.例如,Engine类......你用一个Map实例初始化它并调用它的play方法但是因为你只有一个实例,而且Engine没有必要self.scene_map在一个类中封装那个状态(属性) - 你可以通过那个状态play在你调用它的时候进入方法.

类似地,它的Scene类和子类.是的,Scene该类定义了一个接口("场景将有一个enter方法"),但由于每个场景不包含任何唯一的状态(即属性self),不需要有实例化的对象,你可以更简单地用同样的东西来实现裸功能.

希望在本教程的未来阶段,目的是将这些类开发成更有用的结构,从而证明使用类是正确的.

您可能希望进一步探索这些术语的含义:
http://en.wikipedia.org/wiki/Class_ (computer_science)
http://en.wikipedia.org/wiki/Object_(computer_science)

关于SO的类似问题:
困惑于学习Python的课程困难ex43？