[Python-Dev] new import hooks & zip import (original) (raw)

Just van Rossum just@letterror.com
Thu, 12 Dec 2002 17:25:56 +0100

Guido van Rossum wrote:

Hm, I'd prefer None.

The reason I prefer an exception (any exception, could be a new one) is that you can't return None from an init method, and a class/type is the perfect candidate for a hook (zipimport.zipimporter is one, too). I'd prefer it if people didn't have to write a new method or a separate factory function.

With an exception (especially when you're reusing an existing exception) you never know if it was raised intentionally or whether it means a real (unexpected) error -- in the latter case, swallowing the traceback would be a bad idea because it makes diagnosing the real problem hard. ("Why does my zipimport not work? I don't get any errors, but it doesn't work...")

(I think import.c should print a warning if the zipimport hook couldn't be installed, similar to the site.py warning. The hook itself doesn't invoke any Python code, so an ImportError is a 100% sure sign zipimporter can't handle the path.)

Unless you do imports in the function/class init that is the hook, there's no chance of getting ImportErrors after the hook is installed, so I'm not too worried.

The problem is perhaps comparable to old-style sequence iteration: the getitem implementation could raise a different IndexError than the author intended.

Just