通过字符串引用类名？ [英] Referring to class names through strings?

问题描述

我需要解析一些文本文件，为文本中遇到的各种实体创建对象，并将它们放在一些数据结构（例如，列表）中以供进一步处理。文字范例：

 笔记本电脑
 17dell，重量：12磅
桌面$ b b 24hp 
  

我事先知道文本中可能存在哪些实体，应该有。在这个例子中，我已经有类笔记本电脑和桌面定义（可能是类计算机的子类）。解析器只需要创建对象laptop（'dell'，17，12）和dekstop（'hp'，24）。

我需要从字符串中检索类名，并创建这些类的对象。是否是邪恶的做事方式？如果是这样，什么是最好的方法（使用Python 3.1）？

解决方案

如果类在 computers.py 中定义，比方说，你可以

  import computers 
 getattr（computers，Laptop）（< params>）
  

以实例化 computers.Laptop 。如果它们在您运行代码的同一文件中定义（以便它们是全局变量），则可以执行

  globals（）[Laptop] 
  

或者，如果你想要一个更强大的映射（例如你想要Nettop，Lapbook和笔记本电脑所有实例化笔记本电脑），你可以维护一个映射的字符串到其相应的构造函数，并使用：

  mapping = {Laptop：Laptop，Nettop：Laptop，...} 
映射[Laptop]（）
  

I need to parse some text file, create objects for various entities encountered in the text, and put them in some data structure (e.g., a list) for further processing. Example of the text:

laptop
 17" dell, weight: 12 lb
desktop
 24" hp

I know in advance which entities may exist in the text, and what attributes they are supposed to have. In this example, I would already have classes laptop and desktop defined (probably subclasses of class computer). The parser would just need to create objects laptop('dell', 17, 12), and dekstop('hp', 24).

If I follow this route, I would need to retrieve class names from strings, and create objects of those classes. Is it the Pythonic way of doing things? If so, what's the best approach (using Python 3.1)? If not, what should I do instead?

Thanks!

What

解决方案

If the classes are defined in computers.py, say, you can do

import computers
getattr( computers, "Laptop" )( <params> )

to instantiate a computers.Laptop. If they are defined in the same file that you are running the code in (so that they are global variables), you can do

globals()[ "Laptop" ]

but this is less elegant; it would be nicer to put them in a separate scope.

Alternatively, if you want a more powerful mapping (say you want "Nettop", "Lapbook", and "Laptop" all to instantiate Laptop), you could maintain a mapping of strings to their corresponding constructor and use that:

mapping = { "Laptop": Laptop, "Nettop": Laptop, ... }
mapping[ "Laptop" ]()

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