April 2023
Intermediate to advanced
769 pages
25h 16m
Chinese
Content preview from 流畅的Python（第2版）
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294
｜
第
11
章
11.10
Python
私有属性和
“
受保护
”
的属性
Python
不能像
Java
那样使用
private
修饰符创建私有属性，但是它有一个简单的机制，能
避免子类意外覆盖“私有”属性。
举个例子。有人编写了一个名为
Dog
的类，内部用到了
mood
实例属性，但是没有将其开
放。现在，你创建了
Dog
类的子类
Beagle
。如果你在毫不知情的情况下又创建了名为
mood
的实例属性，那么在继承的方法中就会把
Dog
类的
mood
属性覆盖。这是难以调试的问题。
为了避免这种情况，如果以
__mood
的形式（两个前导下划线，尾部没有或最多有一个下划
线）命名实例属性，那么
Python
就会把属性名存入实例属性
__dict__
中，而且会在前面
加上一个下划线和类名。因此，对
Dog
类来说，
__mood
会变成
_Dog__mood
；对
Beagle
类
来说，
__mood
会变成
_Beagle__mood
。这个语言功能叫
名称改写
（
name mangling
）。
示例
1
1-12
以示例
11-7
中定义的
Vector2d
类为例对名称改写进行了说明。
示例
11-12
私有属性的名称会被“改写”
，在前面加上
_
和类名
>>> v1 = Vector2d(3, 4)
>>> v1.__dict__
{'_Vector2d__y': 4.0, '_Vector2d__x': 3.0}
>>> v1._Vector2d__x
3.0
名称改写是一种安全措施，不能保证万无一失：它的目的是避免意外访问，不能防止故意
做错事。图
1
1-1
也是一种保护装置。 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.