python 面向对象-实例变量、类变量、实例方法、类方法、静态方法

需要搞清楚的是，

1. 实例方法与类方法是什么？类变量和实例变量又是什么？
2. 类方法中如何访问类变量、类方法要如何调用？当然
3. 实例方法中如何访问类变量？能
4. 实例方法访问实例变量，实例方法如何被调用？当然
5. 类方法中能否访问实例变量？不能
6. 对象调用类方法？能
7. 静态方法是什么？装饰器：@staticmethod
8. 静态方法中如何访问类变量和实例变脸、静态方法如何调用？静态方法可以访问类变量、不能访问实例变量，静态方法可以用类名访问，也可以用实例（对象）访问

 

 

1、实例方法与类方法　

实例方法：def do_homework(self):
类方法：def plus_sum(cls):
类变量：  
　　name = ""
   age  = 0
   sum1 = 1

实例变量：
　　self.name
   self.age

注意：决定一个方法是类方法还是实例方法的决定性因素是@classmethod装饰器，跟入参cls没关系。我们的self 可以用cls 代替，也可以用其他入参名代替。

#coding=utf-8
class Student():
    name = ""
    age  = 0
    sum1 = 1
    
    def __init__(self,name,age): #构造函数
        self.name = name
        self.age  = age
    def do_homework(self):#实例方法
        print(self.name +"do homework")
        
    @classmethod
    def plus_sum(cls):
        pass

2、类方法如何访问类变量;类方法如何调用

#coding=utf-8
class Student():
    name = ""
    age  = 0
    sum  = 0
    def __init__(self,name,age): #构造函数
        self.name = name
        self.age  = age
    def do_homework(self):#实例方法
        print(self.name +"do homework")

    @classmethod
    def plus_sum(cls):#类方法
        cls.sum+=1#类方法访问类变量
        print(cls.sum)

student1 = Student("a",18)
Student.plus_sum()#类方法调用，用类名调用类方法
student2 = Student("b",19)
Student.plus_sum()
student3 = Student("c",20)
Student.plus_sum()

# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test6.py"
# 1
# 2
# 3

3、实例方法访问类变量

• 直接访问sum1，报错

  #coding=utf-8
  class Student():
      name = ""
      age  = 0
      sum1 = 0
      
      def __init__(self,name,age): #构造函数
          self.name = name
          self.age  = age
          print(sum1)#直接访问,报错
      def do_homework(self):
          print(self.name +"do homework")
  
  
  student1 = Student("ansonw",26)
  student1.do_homework()
  print(Student.__dict__)
  # Project/python_ToolCodes/test6.py"
  # Traceback (most recent call last):
  #   File "/Users/anson/Documents/Project/python_ToolCodes/test6.py", line 15, in <module>
  #     student1 = Student("ansonw",26)
  #   File "/Users/anson/Documents/Project/python_ToolCodes/test6.py", line 10, in __init__
  #     print(sum1)
  # NameError: global name 'sum1' is not defined

需要怎么访问呢:在类方法中，访问类变量，需要 采用内置变量__class__ 和关键字print(self.__class__.sum1)或者是print(self.sum1) 都可以访问，只是我认为，后面一种访问方法，是用当前对象访问的对象属性，不是类变量；__class__ 代指当前类

#coding=utf-8
class Student():
    name = ""
    age  = 0
    sum1 = 0
    
    def __init__(self,name,age): #构造函数
        self.name = name 
        self.age  = age
        #print(sum1)
        print(self.__class__.sum1)#正确的访问方式
    def do_homework(self):
        print(self.name +"do homework")


# student1 = Student("ansonw",26)
# student1.do_homework()
print(Student.__dict__)
#[Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test6.py"
#0
#ansonwdo homework
#{'__module__': '__main__', 'do_homework': <function do_homework at 0x10cbb3758>, 'name': '', 'age': 0, 'sum1': 0, '__doc__': None, '__init__': <function __init__ at 0x10cbb3140>}
 

4、实例方法访问实例变量，实例方法如何被调用？

#coding=utf-8
class Student():
    name = ""
    age  = 0
    sum  = 0
    def __init__(self,name,age): #构造函数
        self.name = name#实例方法访问实例变量
        self.age  = age
    def do_homework(self):#实例方法
        print("name:"+self.name)#实例方法访问实例变量
        print("this is a object function")

    @classmethod
    def plus_sum(cls):#类方法
        cls.sum+=1
        print(cls.sum)
        print(self.name)
    @staticmethod
    def add(x,y):
        print(x+y)
        print("this is a static method")


student1 = Student("anson",19)
student1.do_homework()#实例方法被调用（被对象调用）
# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test6.py"
# name:anson
# this is a object function

5、类方法中能否访问实例变量？

#coding=utf-8
class Student():
    name = ""
    age  = 0
    sum  = 0
    def __init__(self,name,age): #构造函数
        self.name = name
        self.age  = age
    def do_homework(self):#实例方法
        print(self.name +"do homework")

    @classmethod
    def plus_sum(cls):#类方法
        cls.sum+=1
        print(cls.sum)
        print(self.name)
    @staticmethod
    def add(x,y):
        print(x+y)
        print("this is a static method")


student1 = Student("anson",19)
student1.plus_sum()
Student.plus_sum()

报错

[Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test6.py"
1
Traceback (most recent call last):
  File "/Users/anson/Documents/Project/python_ToolCodes/test6.py", line 25, in <module>
    student1.plus_sum()
  File "/Users/anson/Documents/Project/python_ToolCodes/test6.py", line 16, in plus_sum
    print(self.name)
NameError: global name 'self' is not defined

6、对象调用类方法：

student1.plus_sum()
虽然可以，但是，最好还是不要，因为不伦不类的

#coding=utf-8
class Student():
    name = ""
    age  = 0
    sum  = 0
    def __init__(self,name,age): #构造函数
        self.name = name
        self.age  = age
    def do_homework(self):#实例方法
        print(self.name +"do homework")

    @classmethod
    def plus_sum(cls):#类方法
        cls.sum+=1
        print(cls.sum)

student1 = Student("a",18)
student1.plus_sum()
Student.plus_sum()
student2 = Student("b",19)
Student.plus_sum()
student3 = Student("c",20)
Student.plus_sum()

7、静态方法怎么定义&8、静态方法如何访问类变量、实例变量、静态方法如何被调用

　　同理，运用装饰器：@staticmethod

#coding=utf-8
class Student():
    name = ""
    age  = 0
    sum  = 0
    def __init__(self,name,age): #构造函数
        self.name = name
        self.age  = age
    def do_homework(self):#实例方法
        print(self.name +"do homework")

    @classmethod
    def plus_sum(cls):#类方法
        cls.sum+=1
        print(cls.sum)
    @staticmethod
    def add(x,y)
        pass
（1）静态方法访问类变量：

#coding=utf-8
class Student():
    name = ""
    age  = 0
    sum  = 0
    def __init__(self,name,age): #构造函数
        self.name = name
        self.age  = age
    def do_homework(self):#实例方法
        print(self.name +"do homework")

    @classmethod
    def plus_sum(cls):#类方法
        cls.sum+=1
        print(cls.sum)
    @staticmethod
    def add(x,y)
        print(Student.sum)#静态方法访问类变量
        print("this is a static method")

　　调用静态方法：（1）可以用类名调用、（2）可以用实例来调用

#coding=utf-8
class Student():
    name = ""
    age  = 0
    sum  = 0
    def __init__(self,name,age): #构造函数
        self.name = name
        self.age  = age
    def do_homework(self):#实例方法
        print(self.name +"do homework")

    @classmethod
    def plus_sum(cls):#类方法
        cls.sum+=1
        print(cls.sum)
    @staticmethod
    def add(x,y):
        print(Student.sum)#静态方法访问类变量
        print("this is a static method")
    
Student.add(1,2)#（1）可以用类名调用
student1 = Student("anson",19)
student1.add(1,2)#（2）可以用实例来调用

# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test6.py"
# 0
# this is a static method
# 0
# this is a static method

静态方法访问实例变量

#coding=utf-8
class Student():
    name = ""
    age  = 0
    sum  = 0
    def __init__(self,name,age): #构造函数
        self.name = name
        self.age  = age
    def do_homework(self):#实例方法
        print(self.name +"do homework")

    @classmethod
    def plus_sum(cls):#类方法
        cls.sum+=1
        print(cls.sum)
    @staticmethod
    def add(x,y):
        #print(Student.sum)#静态方法访问类变量
        print(self.name)
        print("this is a static method")
    
Student.add(1,2)
student1 = Student("anson",19)
student1.add(1,2)

报错

# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test6.py"
# Traceback (most recent call last):
#   File "/Users/anson/Documents/Project/python_ToolCodes/test6.py", line 22, in <module>
#     Student.add(1,2)
#   File "/Users/anson/Documents/Project/python_ToolCodes/test6.py", line 19, in add
#     print(self.name)
# NameError: global name 'self' is not defined