简单的方法减少值而不创建新属性？

Question

我正在制作一个程序，在这个程序里你可以发射一个“激光枪”，而我有5发子弹。我正在攻击一个有5点生命值的外星人。最后，我创建了一个玩家，让他发射6次，以检查程序是否正常工作。但是我现在的做法导致子弹数量不会减少。有没有简单的方法解决这个问题，还是说我必须为子弹和生命值分别创建新的属性？这是我现在的代码：

class Player(object):
""" A player in a shooter game. """
def blast(self, enemy, ammo=5):
    if ammo>=1:
        ammo-=1
        print "You have blasted the alien."
        print "You have", ammo, "ammunition left."
        enemy.die(5)
    else:
        print "You are out of ammunition!"


class Alien(object):
    """ An alien in a shooter game. """
    def die(self, health=5):
        if health>=1:
            health-=1
            print "The alien is wounded. He now has", health, "health left."
        elif health==0:
            health-=1
            print "The alien gasps and says, 'Oh, this is it.  This is the big one. \n" \
                  "Yes, it's getting dark now.  Tell my 1.6 million larvae that I loved them... \n" \
                  "Good-bye, cruel universe.'"
        else:
            print "The alien's corpse sits up momentarily and says, 'No need to blast me, I'm dead already!"

# main
print "\t\tDeath of an Alien\n"

hero = Player()
invader = Alien()
hero.blast(invader)
hero.blast(invader)
hero.blast(invader)
hero.blast(invader)
hero.blast(invader)
hero.blast(invader)

raw_input("\n\nPress the enter key to exit.")

Answer 1

我刚刚修改了上面的程序，增加了两个属性，分别叫做弹药（ammo）和生命值（health）。我觉得这样让程序变得简单多了。你可以试着改变这两个属性的初始值，看看会有什么不同的结果。

class Player(object):
""" A player in a shooter game. """ 
def __init__(self, ammo):
    self.ammo = ammo

def blast(self, enemy):
    if enemy.health > 0:
        if self.ammo > 0:
            print "The player has blasted the alien.\n"
            print "The player has", self.ammo, "ammunition left."
            enemy.die()  
        elif self.ammo == 0:
            print "The player can't blast the alien because he is out of ammunition.\n"
        self.ammo -= 1

class Alien(object):
""" An alien in a shooter game. """ 
def __init__(self, health):
    self.health = health

def die(self):
    if self.health > 0:
        self.health -= 1
        print "The alien is wounded. He now has", self.health, "health left.\n"
    if self.health == 0:
        self.health -= 1
        print "The alien gasps and says, 'Oh, this is it. This is the big one. \n"\
          "Yes, it's getting dark now. Tell my 1.6 million larvae that I "\
          "loved them...\nGood-bye, cruel universe.'\n"
    elif self.health < 0:
        print "The alien's corpse sits up momentarily and says, 'No need to blast me, I'm dead already!"

print "\t\tDeath of an Alien\n"
hero = Player(6)
invader = Alien(3)
blast = int(raw_input("How many times do you want to blast the alien? "))
for cnt in range(blast - 1):
    hero.blast(invader)

Answer 2

想一想：可用的弹药数量是玩家状态的一部分。一个对象的状态最好用这个对象的实例变量来表示。所以你不应该把ammo作为blast的参数——在这个方法里应该用self.ammo，而这个值应该在你忘记写的__init__里初始化为5或者其他值;-)。

这并不是在寻找复杂的变通方法来隐藏和存储状态，而是要以最简单、最直接、最有效的方式来处理事情。你为什么会想要其他任何方式呢？！

Answer 3

你需要记录外星人的生命值。现在你做的只是让Alien.die函数里的“生命值”这个局部变量减少。

这里有一段小代码，可以帮助你朝正确的方向前进：

class Alien(object):
    def __init__(self):
        self.health = 5
    def do_damage(self, amount):
        self.health -= amount

玩家的弹药也需要类似的记录。