python实例属性和类属性精讲

Posted 2020-06-22

一：访问与改变

# -*-coding: UTF-8 -*-

class ShuXing(object):

    class_shuxing = "class_shuxing"

    class_shuxing_list = [1, 2, 3]

    def __init__(self):

        self.instance_shuxing = "instance_shuxing"

        self.instance_shuxing_list = [5, 6, 7]

print ShuXing.class_shuxing

print ShuXing.class_shuxing_list

#print ShuXing.instance_shuxing   类名不能访问instance不可变变量

#print ShuXing.instance_shuxing_list  类名不能访问instance可变变量

a = ShuXing()

#instance可以访问任何变量

print a.class_shuxing

print a.class_shuxing_list

print a.instance_shuxing

print a.instance_shuxing_list

print "+++++++++++++++++++"

print "instance gaipian class"

a.class_shuxing = "gaipian class_shuxing"

a.class_shuxing_list.append("gaipian class_shuxing_list")

print ShuXing.class_shuxing  #类不可变变量没改变

print ShuXing.class_shuxing_list  #类可变变量有改变

#print ShuXing.instance_shuxing

#print ShuXing.instance_shuxing_list

a = ShuXing()

print a.class_shuxing

print a.class_shuxing_list   #类可变变量有改变

print a.instance_shuxing

print a.instance_shuxing_list

print "+++++++++++++++++++"

print "class gaipian class"

ShuXing.class_shuxing = "gaipian class_shuxing"

ShuXing.class_shuxing_list.append("gaipian class_shuxing_list")

print ShuXing.class_shuxing   #类不可变变量有改变

print ShuXing.class_shuxing_list  #类可变变量有改变

#print ShuXing.instance_shuxing

#print ShuXing.instance_shuxing_list

a = ShuXing()

print a.class_shuxing   #类不可变变量有改变

print a.class_shuxing_list  #类可变变量有改变

print a.instance_shuxing

print a.instance_shuxing_list

1.Python是一门动态语言，任何实体都可以动态地添加或删除属性。

2.一个类定义了一个作用域。

3.类实例也引入了一个作用域，这与相应类定义的作用域不同。

4.在类实例中查找属性的时候，首先在实例自己的作用域中查找，如果没有找到，则再在类定义的作用域中查找。

5.在对类实例属性进行赋值的时候，实际上会在类实例定义的作用域中添加一个属性（如果还不存在的话），并不会影响到相应类中定义的同名属性。

class ShuXing2(object):

    a = 0

    def __init__(self):

        self.a = 10

        self.b = 20

        

print ShuXing2.a  # 0

#print ShuXing2.b  #类名不能访问instance变量

a = ShuXing2()  

print a.a  # 10

print a.b  # 20

二：用方法访问变量

1 hasattr()：根据输入参数判断某个容器中是否有已该参数为名称的内容，如果有则返回true

2 getattr()：取出容器中以参数为名称的内容

3 setattr()：对容器中以参数为名称的内容进行修改

4 delattr()：删除容器中以参数为名称的内容

class ShuXing2(object):

    a = 0

    def __init__(self):

        self.a = 10

        self.b = 20

a = ShuXing2()

print hasattr(a, ‘a‘)  #True

print getattr(a, ‘a‘)  #10

print setattr(a, ‘a‘, 100)  #None

print getattr(a, ‘a‘) #100

print delattr(a, ‘a‘) #None

print getattr(a, ‘a‘) #0

三：使用特性来管理类实例的属性访问控制

# -*- coding:UTF-8 -*-

class Student(object):

  

    def __init__(self, score):

        self.__score = score

    @property

    def score(self):

        return self.__score

    @score.setter

    def score(self, value):

        if not isinstance(value, int):

            raise ValueError(‘score must be an integer!‘)

        if value < 0 or value > 100:

            raise ValueError(‘score must between 0 ~ 100!‘)

        self.__score = value

s = Student(80)

#print s.__score

s.score = 60

print s.score

s.score = 9999

‘‘‘

60

Traceback (most recent call last):

  File "lizi2.py", line 24, in <module>

    s.score = 9999

  File "lizi2.py", line 16, in score

    raise ValueError(‘score must between 0 ~ 100!‘)

ValueError: score must between 0 ~ 100!

‘‘‘

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