[Python-Dev] Re: Fix import errors to have data (original) (raw)

Jim Fulton jim at zope.com
Tue Jul 27 19:21:15 CEST 2004

Casey Duncan wrote:

On Tue, 27 Jul 2004 12:39:22 -0400 Jim Fulton <jim at zope.com> wrote:

Tim Peters wrote:

[Jim Fulton] ...

No, it won't. For example, suppose foo imports B. B tries to import C, but fails. B is now broken, but it is still importable. Actually,>both foo and B can be imported without errors, even though they are>broken. Then you're proposing a way for a highly knowledgable user to anticipate, and partially worm around, that Python leaves behind insane module objects in sys.modules. No. I'm proposing a way for a Python developer to detect the presence or absence of a module. Hm, perhaps it would be better to provide an API (if there isn't one already) to test whether a module is present. If such an api were to exist, what question exactly would it answer? 1. That there is a module by a particular name that could possibly be imported, but the import may not succeed when actually tried.

Yup

2. There is a module by a particular name which can be imported and the import will not fail.

I would vote for the former, but it might be surprising to run into behavior like this:

sys.hasmodule('foo') True import foo ImportError: foo blew

Of course it would be surprising, because foo would be broken. That's why they call them exceptions. :)

What if there was a new exception ModuleNotFoundError which subclassed ImportError. This would be raised by the import machinery when the module could not be found. Errors during import would continue to raise a standard ImportError.

Yup.

I think this, coupled with Jim's original suggestion and Tim's to prevent broken modules being retained in os.modules would help a lot.

Yup. It would certainly address the imediate problem.

Jim

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