Class three decorator

Method decorative

@classmethod ---> decorative methods, without self property, only property class cls
@staticmethod ---> decorative static method, neither self attributes, it does not have the properties of class cls
@property ---> a method to disguise property

A, @ classmethod

In a class method without object attributes, but use the static properties, then this method is a class method, is decorated classmethod decorator method, there is a default parameter cls, this parameter is the current class!

class A:
    __count = 0
    def __init__(self,name):
        self.name = name
        self.__add_count()  #只要执行init方法实例化对象就会产生调用 __add_count(),从而对静态属性__count操作
    @classmethod
    def __add_count(cls):  #私有方法
        cls.__count += 1  #让这个方法只能在内部被使用
    @classmethod #被classmethod装饰器装饰的方法,都有一个默认的参数,这个参数就是当前类
    def show_count(cls):
        return cls.__count

print(A.show_count())   # 0 类调用show_count方法查看类的静态属性
Sheldon = A('Sheldon')  # 实例化一个对象
print(Sheldon.show_count()) # 1 对象调用show_count方法查看类的静态属性


可以看出调用类方法,可以用对象调用,也可以使用类调用
但是这个方法默认参数永远是当前类的命名空间,而不是对象的

Two, @ staticmethod decorator decoration static method

If the method does not use a class object properties do not use the static properties - Static method, @ staticmethod decoration of this method is actually this way is a common function.

	Common method	Class Methods	Static method
The default parameters	self	cls	no
Variable operation	Operation object properties	Operation class attributes	Neither the operation object properties, nor the operation class attributes
Namespace belongs	class	class	class
Call the method	Objects	Class / object	Class / object
Decorator		@classmethod	@staticmethod

Three. @ Property attribute to a method of disguise

@ Name.setter note, what setter decorative function named, then this function must not modify the properties of the same name in this function

@ Name.deleter caller method to delete properties

示例1
from math import pi
class Circle:
    def __init__(self,r):
        self.r = r

    @property  # 把一个方法伪装成属性 
    def area(self):   # 被property装饰器装饰的方法不能传递除self以外的参数
        return pi*self.r**2

    @property
    def perimeter(self):
        return self.r*pi*2

c1 = Circle(5)
print(c1.area)
c1.r = 10
print(c1.area)   调用的时候不用加()

class Person:
    def __init__(self,name):
        self.__name = name  # 不让外部随便修改
    @property
    def name(self):
        return self.__name

Sheldon = Person('Sheldon')
print(Sheldon.name) #这样写起到不容易被别人修改的作用