类私有成员和类保护成员

class A(object):
    def __init__(self):
        self._protected = 10
        self.__private = 50
    def test(self):
        print self.__private
a =A()
a.test()
print a._protected,a.__private
A._protected
50
10

Traceback (most recent call last):
  File "E:\python\test2.py", line 17, in <module>
    print a._protected,a.__private
AttributeError: 'A' object has no attribute '__private'
Traceback (most recent call last):
  File "E:\python\test2.py", line 20, in <module>
    print A._protected
AttributeError: type object 'A' has no attribute '_protected'

_var ；变量名前一个下划线来定义，此变量为保护成员protected，只有类及其子类可以访问。此变量不能通过from XXX import xxx 导入

__var;变量名前两个下划线来定义，此变量为私有private，只允许类本身访问，连子类都不可以访问。