[Python-ideas] PEP: Distributing a Subset of the Standard Library

[Tomas Orsava]

On 12/06/2016 03:27 AM, Nick Coghlan wrote:
> On 5 December 2016 at 22:53, Tomas Orsava <torsava at redhat.com> wrote:
>> On 12/05/2016 01:42 PM, Nick Coghlan wrote:
>>> Essentially, that would be the "name.missing.py" part of the draft
>>> proposal for optional standard library modules, just with a regular
>>> "name.py" module name and a tweak to getpath.c.
>> To my eye that looks like a complicated mechanism necessitating 
>> changes to
>> several parts of the codebase. Have you considered modifying the default
>> sys.excepthook implementation to read a list of modules and error 
>> messages
>> from a file that was generated during the build process? To me that 
>> seems
>> simpler, and the implementation will be only in one place.
>>
>> In addition, distributors could just populate that file with their data,
>> thus we would have one mechanism for both use cases.
> That's certainly another possibility, and one that initially appears
> to confine most of the complexity to sys.excepthook(). However, the
> problem you run into in that case is that CPython, by default, doesn't
> have any configuration files other than site.py, sitecustomize.py,
> usercustomize.py and whatever PYTHONSTARTUP points to for interactive
> use. The only non-executable one that is currently defined is the
> recommendation to redistributors in PEP 493 for file-based
> configuration of HTTPS-verification-by-default backports to earlier
> 2.7.x versions.
>
> Probably the closest analogy I can think of is the way we currently
> generate _sysconfigdata-<assorted-build-qualifiers>.py in order to
> capture the build time settings such that sysconfig.get_config_vars()
> can report them at runtime.
>
> So using _sysconfigdata as inspiration, it would likely be possible to
> provide a "sysconfig.get_missing_modules()" API that the default
> sys.excepthook() could use to report that a particular import didn't
> work because an optional standard library module hadn't been built.

Quite interesting. And sysconfig.get_missing_modules() wouldn't even 
have to be generated during the build process, because it would be 
called only when the import has failed, at which point it is obvious 
Python was built without said component (like _sqlite3). So do you see 
that as an acceptable solution? Do you prefer the one you suggested 
previously?

Alternatively, can the contents of site.py be generated during the build 
process? Because if some modules couldn't be built, a custom 
implementation of sys.excepthook might be generated there with the data 
for the modules that failed to be built.

Regards,
Tom
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