Python私有属性

在Python中可以通过在属性变量名前加上双下划线定义属性为私有属性，如例子

#! encoding=UTF-8
 
class A:
  def __init__(self):
        
    # 定义私有属性
    self.__name = "琼台博客"
      
    # 普通属性定义
    self.age = 19
 
a = A()
 
# 正常输出
print a.age
 
# 提示找不到属性
print a.__name

执行输出:

19
Traceback (most recent call last):
  File "C:\Users\nicholas\Documents\Aptana Studio 3 Workspace\testa\a.py", line 19, in <module>
    print a.__name
AttributeError: A instance has no attribute '__name'

访问私有属性__name时居然提示找不到属性成员而不是提示权限之类的，于是当你这么写却不报错:

#! encoding=UTF-8
 
class A:
  def __init__(self):
    # 定义私有属性
    self.__name = "琼台博客"
      
    # 普通属性定义
    self.age = 19
         
 
a = A()
 
a.__name = "Jack"
print a.__name # Output: Jack

在Python中就算继承也不能相互访问私有变量，如

#! encoding=UTF-8
 
class A:
  def __init__(self):
        
    # 定义私有属性
    self.__name = "琼台博客"
      
    # 普通属性定义
    self.age = 19
         
 
class B(A):
  def sayName(self):
    print self.__name
         
 
b = B()
b.sayName()

执行结果

Traceback (most recent call last):
  File "C:\Users\nicholas\Documents\Aptana Studio 3 Workspace\testa\a.py", line 19, in <module>
    b.sayName()
  File "C:\Users\nicholas\Documents\Aptana Studio 3 Workspace\testa\a.py", line 15, in sayName
    print self.__name
AttributeError: B instance has no attribute '_B__name'

或者父类访问子类的私有属性也不可以，如

#! encoding=UTF-8
 
class A:
  def say(self):
    print self.name
    print self.__age
         
 
class B(A):
  def __init__(self):
    self.name = "琼台博客"
    self.__age = 20

b = B()
b.say()

执行结果

琼台博客
Traceback (most recent call last):
  File "C:\Users\nicholas\Documents\Aptana Studio 3 Workspace\testa\a.py", line 15, in <module>
    b.say()
  File "C:\Users\nicholas\Documents\Aptana Studio 3 Workspace\testa\a.py", line 6, in say
    print self.__age
AttributeError: B instance has no attribute '_A__age'