python中类的内置属性初探

Posted 2020-10-01

首先，建立一个类，并用该类创建一个对象，分别查看object，类与对象的内置属性

 1 import inspect
 2 
 3 class Foo():
 4     ‘‘‘随便瞎写‘‘‘
 5     group = ‘buluo‘     # 类属性
 6 
 7     @classmethod
 8     def getnum(cls):    # 类方法
 9         return 123
10 
11     def __init__(self):
12         self.name = ‘222‘   # 对象私有属性
13         self.age = 12
14 
15     def changeName(self):   # 对象绑定方法
16         self.name = self.__class__.getnum()
17 
18 # 创建类，并获取三者内置属性
19 a = Foo();
20 inspect.getmembers(object):
21 inspect.getmembers(Foo):
22 inspect.getmembers(a):

实例类

 1 # slot wrapper "插口"包装，继承object类之后进行重写，
 2 
 3 (‘__class__‘, <class ‘type‘>)
 4 (‘__delattr__‘, <slot wrapper ‘__delattr__‘ of ‘object‘ objects>)
 5 (‘__dir__‘, <method ‘__dir__‘ of ‘object‘ objects>)
 6 (‘__doc__‘, ‘The most base type‘)
 7 (‘__eq__‘, <slot wrapper ‘__eq__‘ of ‘object‘ objects>)
 8 (‘__format__‘, <method ‘__format__‘ of ‘object‘ objects>)
 9 (‘__ge__‘, <slot wrapper ‘__ge__‘ of ‘object‘ objects>)
10 (‘__getattribute__‘, <slot wrapper ‘__getattribute__‘ of ‘object‘ objects>)
11 (‘__gt__‘, <slot wrapper ‘__gt__‘ of ‘object‘ objects>)
12 (‘__hash__‘, <slot wrapper ‘__hash__‘ of ‘object‘ objects>)
13 (‘__init__‘, <slot wrapper ‘__init__‘ of ‘object‘ objects>)
14 (‘__init_subclass__‘, <built-in method __init_subclass__ of type object at 0x1DFFADB8>)
15 (‘__le__‘, <slot wrapper ‘__le__‘ of ‘object‘ objects>)
16 (‘__lt__‘, <slot wrapper ‘__lt__‘ of ‘object‘ objects>)
17 (‘__ne__‘, <slot wrapper ‘__ne__‘ of ‘object‘ objects>)
18 (‘__new__‘, <built-in method __new__ of type object at 0x1DFFADB8>)
19 (‘__reduce__‘, <method ‘__reduce__‘ of ‘object‘ objects>)
20 (‘__reduce_ex__‘, <method ‘__reduce_ex__‘ of ‘object‘ objects>)
21 (‘__repr__‘, <slot wrapper ‘__repr__‘ of ‘object‘ objects>)
22 (‘__setattr__‘, <slot wrapper ‘__setattr__‘ of ‘object‘ objects>)
23 (‘__sizeof__‘, <method ‘__sizeof__‘ of ‘object‘ objects>)
24 (‘__str__‘, <slot wrapper ‘__str__‘ of ‘object‘ objects>)
25 (‘__subclasshook__‘, <built-in method __subclasshook__ of type object at 0x1DFFADB8>)

object内置属性

 Foo类的内置属性，去掉object重复的，可以看到，多了一个__dict__以及其他方法与属性 

(‘__class__‘, <class ‘type‘>)
(‘__dict__‘, mappingproxy({‘__module__‘: ‘__main__‘, ‘__doc__‘: ‘随便瞎写‘, ‘group‘: ‘buluo‘, ‘getnum‘: <classmethod object at 0x02237770>, ‘__init__‘: <function Foo.__init__ at 0x022BA078>, ‘changeName‘: <function Foo.changeName at 0x022BA0C0>, ‘__dict__‘: <attribute ‘__dict__‘ of ‘Foo‘ objects>, ‘__weakref__‘: <attribute ‘__weakref__‘ of ‘Foo‘ objects>}))
(‘__doc__‘, ‘随便瞎写‘)
(‘changeName‘, <function Foo.changeName at 0x022BA0C0>)　　# 对于类来说，changeName为类的普通方法
(‘getnum‘, <bound method Foo.getnum of <class ‘__main__.Foo‘>>)　　# 用@staticmethod装饰器的getnum函数为类的绑定方法
(‘group‘, ‘buluo‘)

 Foo对象的内置属性

(‘__class__‘, <class ‘__main__.Foo‘>)
(‘__dict__‘, {‘name‘: ‘222‘, ‘age‘: 12})　　# 对象的__dict__ 只包含私有的属性

# 类的静态方法或者方法，对于对象来说，都为绑定方法，绑定对象不同，一个是Foo object，一个是class.__main__.Foo
(‘changeName‘, <bound method Foo.changeName of <__main__.Foo object at 0x02242390>>)　　
(‘getnum‘, <bound method Foo.getnum of <class ‘__main__.Foo‘>>)

(‘group‘, ‘buluo‘)
(‘name‘, ‘222‘) 
(‘age‘, 12)

 

总结：1.__dict__为对象的私有属性，对对象来说，则为私有变量（方法并非私有，而是绑定），

　　　　　　　　　　　　　　　　  对元类的对象（即metaclass为type的类），则为__module__,__doc__,属性、方法以及一个弱引用

　　　2.对象的私有属性不单单会在__dict__中出现，在对象的内置属性内也会存在，而__dict__的存在为了加快处理速度，屏蔽其他不需要注意的属性

 

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疑问：私有属性在__dict__以及内置属性中都出现，对象的大量创建会导致内存压力，如何解决，使用__slots__

通过__slots__将属性固定

 1 class Foo_slot():
 2     group = ‘buluo‘
 3     __slots__ = [‘name‘, ‘age‘]
 4 
 5     @classmethod
 6     def getnum(cls):    # 类方法
 7         return 123
 8 
 9     def changeName(self):   # 对象绑定方法
10         self.age = self.__class__.getnum()

测试类

 带有__slots__Foo类的内置属性，__dict__不存在

(‘__slots__‘, [‘name‘, ‘age‘])

# __slots__中的变量，类型为member，“成员”，类似C中的结构体
(‘age‘, <member ‘age‘ of ‘Foo_slot‘ objects>)
(‘name‘, <member ‘name‘ of ‘Foo_slot‘ objects>)

(‘group‘, ‘buluo‘)    # 类的普通变量不变

# 方法不受影响
(‘changeName‘, <function Foo_slot.changeName at 0x01F0D150>)
(‘getnum‘, <bound method Foo_slot.getnum of <class ‘__main__.Foo_slot‘>>)

带有__slots__Foo类的对象的内置属性

(‘__slots__‘, [‘name‘, ‘age‘]) # 与普通类不同，在内置属性中并未带有属性，请查看上面“Foo对象的内置属性”中，包含了属性以及属性值

(‘changeName‘, <bound method Foo_slot.changeName of <__main__.Foo_slot object at 0x021B23F0>>)
(‘getnum‘, <bound method Foo_slot.getnum of <class ‘__main__.Foo_slot‘>>)

(‘group‘, ‘buluo‘)    # 类的属性不受影响
# 除了类的属性之外，私有属性并没有在对象的内置属性中出现，可见slots的类，去掉__dict__与私有方法，确实在内存中会节省一部分空间