Python类方法、实例方法、静态方法和属性方法详解

#实验证明eat静态方法里不能传self对象，因此无法调用实例变量


import requests,json
class Dog(object):
    food='牛肉'
    name='大黄狗'
    def __init__(self, name):
        self.name = name
    @staticmethod
    def eat(self):
        print('%s eat %s' %(self.name,Dog.food))
d = Dog("拉布拉多")
d.eat()
Dog.eat()

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
Traceback (most recent call last):
  File "C:/Users/wangli/PycharmProjects/Test/Test/test.py", line 104, in <module>
    d.eat()
TypeError: eat() missing 1 required positional argument: 'self'

Process finished with exit code 1

#实验证明eat静态方法，可由类和实例调用，可使用类变量



class Dog(object):
    food='牛肉'
    name='大黄狗'
    def __init__(self, name):
        self.name = name
    @staticmethod
    def eat(who):
        print('%s %s eat %s' %(who,Dog.name,Dog.food))
d = Dog("拉布拉多")
d.eat('橙子家')
Dog.eat('橘子家')

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
橙子家 大黄狗 eat 牛肉
橘子家 大黄狗 eat 牛肉

Process finished with exit code 0

实验证明：
通过cls参数传递当前类对象，不需要实例化，直接类名.方法名() 通过类对象和类对象实例访问

import requests,json
class Dog(object):
    food='牛肉'
    name='大黄狗'
    def __init__(self, name):
        self.name = name
    @classmethod
    def eat(cls,who):
        print('%s %s eat %s' %(who,cls.name,Dog.food))
d = Dog("大白狗")
d.eat('橙子家')
Dog.eat('橘子家')

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
橙子家 大黄狗 eat 牛肉
橘子家 大黄狗 eat 牛肉

Process finished with exit code 0

实验证明：
类方法只能访问类变量，不能访问实例变量



class Dog(object):
    food='牛肉'
    #name='大黄狗'
    def __init__(self, name):
        self.name = name
    @classmethod
    def eat(self,who):
        print('%s %s eat %s' %(who,self.name,Dog.food))
d = Dog("大白狗")
d.eat('橙子家')
Dog.eat('橘子家')


"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
Traceback (most recent call last):
  File "C:/Users/wangli/PycharmProjects/Test/Test/test.py", line 104, in <module>
    d.eat('橙子家')
  File "C:/Users/wangli/PycharmProjects/Test/Test/test.py", line 102, in eat
    print('%s %s eat %s' %(who,self.name,Dog.food))
AttributeError: type object 'Dog' has no attribute 'name'

Process finished with exit code 1

实验证明：
实例方法可调用类变量和实例变量

class Dog(object):
    food='牛肉'
    name='大黄狗'
    def __init__(self, name):
        self.name = name
    def eat(self,who):  #实例方法
        print('%s %s eat %s' %(who,self.name,Dog.food))
d = Dog("大白狗")
d.eat('橙子家')

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
橙子家 大白狗 eat 牛肉

Process finished with exit code 0

给 属性方法赋值

class Dog(object):
    def __init__(self, name):
        self.name = name
        self.__food = None
    @property
    def eat(self):
        print('%s eat %s' %(self.name,self.__food))
    @eat.setter
    def eat(self, food):
        self.__food = food
d = Dog("labuladuo")
d.eat
d.eat = "baozi"
d.eat

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
wang eat None
wang eat baozi

Process finished with exit code 0

属性方法应用场景
比如 ，你想知道一个航班当前的状态，是到达了、延迟了、取消了、还是已经飞走了， 想知道这种状态你必须经历以下几步:

1. 连接航空公司API查询

2. 对查询结果进行解析 

3. 返回结果给你的用户

因此这个status属性的值是一系列动作后才得到的结果，所以你每次调用时，其实它都要经过一系列的动作才返回你结果，但这些动作过程不需要用户关心， 用户只需要调用这个属性就可以


import requests,json
class Flight(object):
    def __init__(self,name):
        self.flight_name = name
    def checking_status(self):
        print("checking flight %s status " % self.flight_name)
        return  1
    @property
    def flight_status(self):
        status = self.checking_status()
        if status == 0 :
            print("flight got canceled...")
        elif status == 1 :
            print("flight is arrived...")
        elif status == 2:
            print("flight has departured already...")
        else:
            print("cannot confirm the flight status...,please check later")
    @flight_status.setter
    def flight_status(self,status):
        print('fight %s has changed status to %s'%(self.flight_name,status))
f = Flight("CA980")
f.flight_status
f.flight_status=2



"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
checking flight CA980 status 
flight is arrived...
fight CA980 has changed status to 2

Process finished with exit code 0