Question

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

Answer 1

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" ]()