April 2023
Intermediate to advanced
769 pages
25h 16m
Chinese
Content preview from 流畅的Python（第2版）
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类元编程
｜
725
➐
……把字段的
storage_name
追加到一个列表中……
➑
……用于填充
cls_dict
（待构造类的命名空间）中的
__slots__
项。
➒
最后，调用
super().__new__
。
metaclass/checkedlib.py
的最后一部分是
Checked
基类。这个库的用户通过子类化该基类增
强自己定义的类，例如
Movie
。
这一版
Checked
类，除了以下
3
处改动之外，其他代码与
initsub/checkedlib.py
中一样（参
见示例
24-5
和示例
24-6
）。
1.
添加一个空的
__slots__
属性，告诉
CheckedMeta.__new__
，这个类不需要特殊处理。
2.
删除
__init_subclass__
。相关工作现在交给
CheckedMeta.__new__
。
3.
删除
__setattr__
。为用户定义的类添加
__slots__
之后，无法设置未声明的属性了，
因此这个方法也就多余了。
示例
24-23
是最终版
Checked
类的完整代码。
示例
24-23
metaclass/checkedlib.py
：
Checked
基类
class Checked(metaclass=CheckedMeta):
__slots__ = () # 跳过CheckedMeta.__new__的处理
@classmethod
def _fields(cls) -> dict[str, type]:
return get_type_hints(cls)
def __init__(self, ...
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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.