staticmethod classmethod property方法

@staticmethod 静态方法

函数修饰符，用来修饰一个函数，类似于装饰器

class Dog(object):
    def __init__(self,name):
        self.name = name

    def eat(self,food):
        print('%s is eating %s'%(self.name,food))

d = Dog('二哈')
d.eat('包子')      #二哈 is eating 包子

 eat()方法上面加上 @staticmethod

class Dog(object):
    def __init__(self,name):
        self.name = name
    @staticmethod
    def eat(self,food):
        print('%s is eating %s'%(self.name,food))

d = Dog('二哈')
d.eat('包子')  #TypeError: eat() missing 1 required positional argument: 'food'

 提示 food 少传递一个参数

删除food参数尝试下

class Dog(object):
    def __init__(self,name):
        self.name = name
    @staticmethod
    def eat(self):
        print('%s is eating %s'%(self.name,'包子'))

d = Dog('二哈')
d.eat()  #TypeError: eat() missing 1 required positional argument: 'self'

 提示少一个位置参数self ，self默认不是自动传进去的吗，静态方法就是截断方法与类的联系，就是说eat在这里就只是一个单纯的函数。

调用方式：类名。静态方法（） 也可以用对象调用方法的方式。

class Dog(object):
    def __init__(self,name):
        self.name = name
    @staticmethod
    def eat():
        print('%s is eating %s'%('5545','包子'))

d = Dog('二哈')
d.eat()    #5545 is eating 包子
Dog.eat() #5545 is eating 包子

 要在静态方法里面调用self，就必须把self本身传进去

class Dog(object):
    def __init__(self,name):
        self.name = name
    @staticmethod
    def eat(self):
        print('%s is eating %s'%(self.name,'包子'))

d = Dog('二哈')
d.eat(d)       #二哈 is eating 包子

 静态方法名义上归类管理，实际上调用不了类或者实例的任何属性。

@classmethod  类方法

函数修饰符，同样用来装饰函数

class Dog(object):
    def __init__(self,name):
        self.name = name
    @classmethod
    def eat(self):
        print('%s is eating %s'%(self.name,'包子'))

d = Dog('二哈')
d.eat() #AttributeError: type object 'Dog' has no attribute 'name'

 尝试访问类变量

class Dog(object):
    name= '秋田'
    def __init__(self,name):
        self.name = name
    @classmethod
    def eat(self):
        print('%s is eating %s'%(self.name,'包子'))

d = Dog('二哈')
d.eat() #秋田 is eating 包子

类方法只能访问类变量，不能访问实例变量。

property 属性方法

class Dog(object):
    name= '秋田'
    def __init__(self,name):
        self.name = name
    @property
    def eat(self):
        print('%s is eating %s'%(self.name,'包子'))

d = Dog('二哈')
d.eat() #TypeError: 'NoneType' object is not callable

 去掉括号

class Dog(object):
    name= '秋田'
    def __init__(self,name):
        self.name = name
    @property
    def eat(self):
        print('%s is eating %s'%(self.name,'包子'))

d = Dog('二哈')
d.eat  #二哈 is eating 包子

 把一个方法变成静态属性

作为一个属性，如果有参数要怎么传递？

既然是属性就是可以赋值的。

class Dog(object):
    name= '秋田'
    def __init__(self,name):
        self.name = name
    @property
    def eat(self,food):
        print('%s is eating %s'%(self.name,food))

d = Dog('二哈')
d.eat = '包子' #AttributeError: can't set attribute

 直接赋值也是不可以的，同样需要装饰下

class Dog(object):
    name= '秋田'
    def __init__(self,name):
        self.name = name
        self._food = None
    @property
    def eat(self):
        print('%s is eating %s'%(self.name,self._food))
    @eat.setter
    def eat(self,food):
        print('set food is',food)
        self._food = food

d = Dog('二哈')
d.eat = '包子' #set food is 包子
d.eat           #二哈 is eating 包子

 属性赋值会触发 @eat.setter 下的 eat()方法。

删除属性

class Dog(object):
    name= '秋田'
    def __init__(self,name):
        self.name = name
        self.__food = None
    @property
    def eat(self):
        print('%s is eating %s'%(self.name,self._food))
    @eat.setter
    def eat(self,food):
        print('set food is',food)
        self.__food = food
 
d = Dog('二哈')
d.eat = '包子'
d.eat
del d.eat #AttributeError: 'Dog' object has no attribute '_food'

 默认是不能删除的，如果非要删除就要重写

class Dog(object):
    name= '秋田'
    def __init__(self,name):
        self.name = name
        self.__food = None
    @property
    def eat(self):
        print('%s is eating %s'%(self.name,self.__food))
    @eat.setter
    def eat(self,food):
        print('set food is',food)
        self.__food = food

    @eat.deleter
    def eat(self):
        del self.__food
        print('删除成功')

d = Dog('二哈')
d.eat = '包子' set food is 包子
d.eat  # 二哈 is eating 包子
del d.eat  # 删除成功
d.eat   # AttributeError: 'Dog' object has no attribute '_Dog__food'

 d.eat调用了@property下的eat  因为这个方法里面有调用self.__food 而这个属性被删除了

有些场景不能简单的通过定义静态属性来实现的。所有要把方法做成属性。比如有些接口的API。