April 2023
Intermediate to advanced
769 pages
25h 16m
Chinese
Content preview from 流畅的Python（第2版）
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695
第 24章
类元编程
所有人都知道调试程序的难度是写程序的两倍。所以如果你写程序的时候尽可能
地“精明”，那么未来将如何调试它？
——
Brian W
. Kernighan
和
P. J. Plauger
《编程格调》
类元编程指在运行时创建或定制类的技艺。在
Python
中
，类是一等对象，因此任何时候都
可以使用函数新建类，无须使用
class
关键字。类装饰器也是函数，不过能够审查、修改，
甚至把被装饰的类替换成另一个类。最后，元类是类元编程最高级的工具：使用元类可以
创建具有某种特质的全新类，例如前面讲过的抽象基类。
元类功能强大，但是难以掌握。类装饰器能使用更简单的方式解决很多同类问题。此外，
Python 3.6
实现的“
PEP
487
—
Simpler customization of class creation
”提供了一些特殊方法，
可以完成以前需要元类或类装饰器才能完成的任务。
1
本章按照复杂度从易到难讲解类元编程技术。
这是一个令人兴奋的话题，很容易让人忘乎所以。因此，我必须提出以下
警告。
为了可读性和可维护性，或许应该避免在应用程序代码中使用本章讲解的
技术。
反之，如果想编写下一个引起轰动的
Python
框架
，那么肯定离不开这些
工具。
注
1
：
并不是说
PEP 487
会破坏使用那些功能的代码。只是在
Python 3.6
以前使用类装饰器或元类编写的
代码，现在可以使用普通的类重构，写出的代码更简单且更高效。
696
｜
第
24
章
24.1
本章新增内容
本书第
1
版“类元编程”一章中的所有代码依然能正常运行。然而，与 ...
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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.