[Python-Dev] Re: Fix import errors to have data
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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