__slots__作用

1.减少内存消耗

2.限制添加类属性及类初始化参数

实现__slots__

1.限制单个类属性

class Base(object):
    __slots__ = ['name']
　　pass


B = Base()
B.name = 'John'

2.限制多个类属性，在__slots__的列表中继续添加即可

class Base(object):
    __slots__ = ['name','age']
　　pass


B = Base()
B.name = 'John'
B.age = 18

当添加类属性为非__slots__列表中的参数，会报错 AttributeError: 'Base' object has no attribute 'name1'

class Base(object):
    __slots__ = ['name']

    pass
B = Base()
B.name1 = 'John'  #AttributeError: 'Base' object has no attribute 'name1'

同样，__slots__会限制类初始化参数

class Base(object):
    __slots__ = ['name']

    def __init__(self,name,age):
        self.name = name
        self.age = age
    pass

B = Base('John',18) #AttributeError: 'Base' object has no attribute 'age'

节约内存

由于默认情况下每个类都会有一个dict,通过__dict__访问，这个dict维护了这个实例的所有属性。如果类中使用__slots__时，该对象不会自动产生__dict__属性

class Base(object):
    __slots__ = ['name']

    def __init__(self,name):
        self.name = name
    pass

B = Base('John')

print(B.__dict__)  #打印报错AttributeError: 'Base' object has no attribute '__dict__'

class Base(object):
    # __slots__ = ['name']

    def __init__(self,name):
        self.name = name
    pass

B = Base('John')

print(B.__dict__) # {'name': 'John'}