【python】详解类class的通过__slots__限制类实例对象的属性（七）

当我们通过一个类创建了实例之后，仍然可以给实例添加属性，但是这些属性只属于这个实例。有些时候，我们可以需要限制类实例对象的属性，这时就要用到类中的_ _slots _ _ 属性了。_ _ slots_ _属性对于一个tuple，只有这个tuple中出现的属性可以被类实例使用。

class person(object):
    __slots__ = ("name", "age","weight")
    def __init__(self, name, age, weight):
        self.name = name
        self.age = age
        self.weight = weight
Bruce = person("Bruce", 25,60)        
print("%s is %d years old and he weights %s" %(Bruce.name, Bruce.age,Bruce.weight))
Bruce.tall = 180

输出结果：

Bruce is 25 years old and he weights 60
Traceback (most recent call last):

  File "", line 1, in <module>
    runfile('C:/Users/BruceWong/.spyder-py3/类的__slots__.py', wdir='C:/Users/BruceWong/.spyder-py3')

  File "C:\Anaconda3\lib\site-packages\spyder\utils\site\sitecustomize.py", line 866, in runfile
    execfile(filename, namespace)

  File "C:\Anaconda3\lib\site-packages\spyder\utils\site\sitecustomize.py", line 102, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)

  File "C:/Users/BruceWong/.spyder-py3/类的__slots__.py", line 17, in <module>
    Bruce.tall = 180

AttributeError: 'person' object has no attribute 'tall'

person类实例化后，Bruce不能添加新的属性，_ _ slots_ _属性对于一个tuple属性赋值，只有这个tuple中出现的属性可以被类实例使用

• 使用_ _ slots _ _ 要注意， _ slots_ _定义的属性仅对当前类的实例起作用，对继承的子类实例是不起作用的,不会限制继承的子类实例化再添加新的属性

class human(object):
    __slots__ = ("name", "age","weight")
class person(human):
    #__slots__ = ("name", "age","weight")
    def __init__(self, name, age, weight):
        self.name = name
        self.age = age
        self.weight = weight
Bruce = person("Bruce", 25,60)        
print("%s is %d years old and he weights %s" %(Bruce.name, Bruce.age,Bruce.weight))
Bruce.tall = 180

输出结果，此时添加Bruce.tall =180 属性就不会报错：

Bruce is 25 years old and he weights 60

• 如果子类本身也有_ _ slots_ _ 属性，子类的属性就是自身的 _ _ slots _ _ 加上父类的_ _ slots_ _

class human(object):
    __slots__ = ("tall")
class person(human):
    __slots__ = ("name", "age","weight")
    def __init__(self, name, age, weight):
        self.name = name
        self.age = age
        self.weight = weight
Bruce = person("Bruce", 25,60)        
print("%s is %d years old and he weights %s" %(Bruce.name, Bruce.age,Bruce.weight))
Bruce.tall = 180
print("%s is %d years old and he weights %s and he\'s tall is %s" %(Bruce.name, Bruce.age,Bruce.weight,Bruce.tall))
Bruce.appearance = 'handsome'

输出结果：

Bruce is 25 years old and he weights 60
Bruce is 25 years old and he weights 60 and he's tall is 180
Traceback (most recent call last):

  File "", line 1, in 
    runfile('C:/Users/BruceWong/.spyder-py3/类的__slots__.py', wdir='C:/Users/BruceWong/.spyder-py3')

  File "C:\Anaconda3\lib\site-packages\spyder\utils\site\sitecustomize.py", line 866, in runfile
    execfile(filename, namespace)

  File "C:\Anaconda3\lib\site-packages\spyder\utils\site\sitecustomize.py", line 102, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)

  File "C:/Users/BruceWong/.spyder-py3/类的__slots__.py", line 26, in 
    Bruce.appearance = 'handsome'

AttributeError: 'person' object has no attribute 'appearance'

父类和子类限制的元组里面的变量属性都是可以生成调用的。appearance既不在父类也不再继承的子类的元组列表里，不能生成