python - 如何获取对象属性的引用？

Question

我正在寻找一种方法来根据解析为方法的值来更改对象属性。例如:

class Character(object):
    def __init__(self, hp, mp, st, ag):
        self.hp = hp
        self.mp = mp
        self.st = st
        self.ag = ag

    def increase_stat(self, stat, value):
        ''' Increase one of the attributes
            (hp, mp, st, ag) by a given value.
        '''
        stat_dict = {'hp': self.hp,
                     'mp': self.mp,
                     'st': self.st,
                     'ag': self.ag}
        stat_attr = stat_dict.get(stat)
        # below should be equivalent to self.hp += value
        stat_attr += value


hero = Character(hp=10, mp=4, st=3, ag=2)
hero.increase_stat(stat='hp', value=2)
# this should increase the hp by 2
print(hero.hp == 12)

我知道这不起作用，因为 stat_dict.get(stat) 返回 self.hp 指向的值而不是实际的 self.hp 对象。

当前解决方案

我没有将属性作为字典的值，而是使用增加每个单独统计数据的方法。

class Character(object):
    def __init__(self, hp, mp, st, ag):
        self.hp = hp
        self.mp = mp
        self.st = st
        self.ag = ag

    def increase_stat(self, stat, value):
        ''' Increase one of the attributes
            (hp, mp, st, ag) by a given value.
        '''
        stat_method_dict = {'hp': self._increase_hp,
                            'mp': self._increase_mp,
                            'st': self._increase_st,
                            'ag': self._increase_ag}
        alter_stat_method = stat_method_dict.get(stat)
        alter_stat_method(value)

    def _increase_hp(self, value):
        self.hp += value

    def _increase_mp(self, value):
        self.mp += value

    def _increase_st(self, value):
        self.st += value

    def _increase_ag(self, value):
        self.ag = value


hero = Character(hp=10, mp=4, st=3, ag=2)
hero.increase_stat(stat='hp', value=2)
# this should increase the hp by 2
print(hero.hp == 12)

我的问题是它是重复的，如果我决定向类添加更多属性/统计信息，那么这只会增加重复方法的数量。我想知道是否有比我上面提供的更好的解决方案？

解决方案

现在看来非常明显。谢谢大家。

class Character(object):
    def __init__(self, hp, mp, st, ag):
        self.hp = hp
        self.mp = mp
        self.st = st
        self.ag = ag

    def increase_stat(self, stat, value):
        ''' Increase one of the attributes
            (hp, mp, st, ag) by a given value.
        '''
        current = getattr(self, stat) 
        setattr(self, stat, current+value)

Answer 1

你的统计字典确实没有任何作用。使用 getattr 和 setattr 动态操作属性。所以，类似于:

def increase_stat(self, stat, value):
    setattr(self, stat, value + getattr(self, stat))

所以，例如:

In [30]: class Dummy:
    ...:     def __init__(self):
    ...:         self.intelligence = 0
    ...:         self.strength = 10
    ...:         self.hp = 100
    ...:     def increase_stat(self, stat, value):
    ...:         setattr(self, stat, value + getattr(self, stat))
    ...:

In [31]: d = Dummy()

In [32]: d.strength
Out[32]: 10

In [33]: d.increase_stat('strength', 10)

In [34]: d.strength
Out[34]: 20

也许更容易阅读:

def increase_stat(self, stat, value):
    current = getattr(self, stat)
    setattr(self, stat, current + value)

请注意，这比直接操作实例 __dict__ 更好，后者会因 property 对象等描述符而中断。更不用说没有 __dict__ 的对象，例如带有 __slots__

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