如何获取对对象属性的引用？

Question

我正在寻找一种根据解析到方法的值来改变objects属性的方法。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)

我知道这不符合统计_听写（stat）返回值自身.hp是指向而不是实际的自身.hp对象。你知道吗

当前解决方案

我没有将属性作为dict的值，而是使用增加每个stat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的属性/统计信息，那么这只会增加重复方法的数量。我想知道是否有一个更好的解决办法，比我已经产生了上述？你知道吗

解决方案

现在看来很明显。谢谢大家。你知道吗

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

你的统计数字真的没用。使用getattr和setattr动态操作属性。比如说：

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

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

或许更容易阅读：

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

注意，这比直接操作实例__dict__要好，后者将与property对象之类的描述符分离。更不用说没有__dict__的对象了，比如带有__slots__的类型

Answer 2

您可以使用__setitem__方法获得更简洁的解决方案：

class Character(object):
  def __init__(self, *args):
     self.__dict__ = dict(zip(['hp', 'mp', 'st', 'ag'], args))
  def __setitem__(self, name, val):
     self.__dict__[name] += val

hero = Character(10, 4, 3, 2)
hero['hp'] = 2
print(hero.hp)

输出：

12

但是，也可以使用自定义方法来实现此策略：

class Character(object):
  def __init__(self, *args):
     self.__dict__ = dict(zip(['hp', 'mp', 'st', 'ag'], args))
  def increase_stat(self, stat, value):
     self.__dict__[stat] += value

hero = Character(10, 4, 3, 2)
hero.increase_stat(stat='hp', value=2)

输出：

12