python实例属性和类属性精讲
一：访问与改变# -*-coding: UTF-8 -*-
class ShuXing(object):
class_shuxing = "class_shuxing"
class_shuxing_list =
def __init__(self):
self.instance_shuxing = "instance_shuxing"
self.instance_shuxing_list =
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!
'''
四：描述符管理“类属性”（不是类实例）访问
class Descriptor(object):
def __init__(self):
self._name = ''
def __get__(self, instance, owner):
print "Getting: %s" % self._name
return self._name
def __set__(self, instance, name):
print "Setting: %s" % name
self._name = name.title()
def __delete__(self, instance):
print "Deleting: %s" % self._name
del self._name
class Person(object):
name = Descriptor()
def__init__(self, name):
self._name = name
>>> user = Person()
>>> user.name = 'john smith'
Setting: john smith
>>> user.name
Getting: John Smith
'John Smith'
>>> del user.name
Deleting: John Smith
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