python 实例属性之单，双下划线

具体区别看下面例子

 1 class A:
 2     def __init__(self,name=‘Andy‘):
 3         self._name = name
 4
 5 class B:
 6     def __init__(self,name = ‘Jack‘,age=19):
 7         self.__name = name  # 私有属性(变量)，只有类对象自己能访问，子类也不能访问
 8         self._age = age     # 保护变量，类，及子类对象可以访问
 9
10 class C(B):
11     def h(self):
12         print(‘hello‘)
13
14 a = A()
15 b = B()
16 c = C()
17 print(a._name)  # 输出Adny
18 print(b._B__name)   # 私有属性在类外的访问方式：对象._类__属性名
19 print(c._age)   # 输出19
20 print(c._C__name)   # AttributeError: ‘C‘ object has no attribute ‘_C__name‘子类不能访问