[Python-ideas] Better error messages for missing optional stdlib packages

[Marcus Harnisch]

Hi Steven

On 10/04/2018 12:32 AM, Steven D'Aprano wrote:
> On Wed, Oct 03, 2018 at 10:29:45PM +0200, Marcus Harnisch wrote:
>> When trying to import lzma on one of my machines, I was suprised to get
>> a normal import error like for any other module. According to the docs
>> lzma has been part of stdlib since 3.3. Further digging revealed that
>> the error is due to the fact that xz wasn't compiled in when building
>> Python. Since I suspect that there are other optional stdlib modules,
>> this made me think whether the message in those cases should look a
>> little more polished. Perhaps installing a stub module that prints some
>> informative text before raising the relevant exception or similar.
> This sounds to me like something that the various Python distributors
> could do, e.g. Activestate, the Linux distros, etc. Especially since
> they're the ones compiling Python, they can control whether or not XY is
> supplied or not.
I'd argue that it is Python that creates the dependency and is therefore 
responsible to handle this gracefully. But, I guess having this 
documented first is the most important step before discussing further 
measures.
>> Also, maybe add a little note in the docs, stating that despite being
>> part of stdlib this module might not be available on all systems.
> That should be uncontroversial. Raise an issue on the bug tracker for
> that, or a patch on Github.
Done. https://bugs.python.org/issue34895

Thanks,
Marcus