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

27 Jul 2004


      Casey Duncan wrote:
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On Tue, 27 Jul 2004 12:39:22 -0400
Jim Fulton  wrote:
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Tim Peters wrote:
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[Jim Fulton]
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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
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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:
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sys.hasmodule('foo')
True
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import foo
ImportError: foo blew
Of course it would be surprising, because foo would be broken.
That's why they call them exceptions. :)
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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.
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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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