[Python-ideas] PEP 4XX: Adding sys.implementation

[Eric Snow]

On Tue, May 1, 2012 at 8:37 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On Wed, May 2, 2012 at 11:09 AM, Steven D'Aprano <steve at pearwood.info> wrote:
>> Syntax-wise, dotted name access seems right to me for this, similar to
>> sys.float_info. If you know a field exists, sys.implementation.field is much
>> nicer than sys.implementation['field'].
>>
>> I hate to admit it, but I'm starting to think that the right solution here
>> is something like a dict with dotted name access.
>
> Whereas I'm thinking it makes sense to explicitly separate out
> "standard, must be defined by all conforming Python implementations"
> and "implementation specific extras"
>
> Under that model, we'd add an extra "metadata" field at the standard
> level to hold implementation specific fields. The initial set of
> standard fields would then be:
>
> name: the name of the implementation (e.g. "CPython", "IronPython",
> "PyPy", "Jython")
> version: the version of the implemenation (in sys.version_info format)
> cache_tag: the identifier used by importlib when caching bytecode
> files in __pycache__ (set to None to disable bytecode caching)
> metadata: a dict containing arbitrary additional information about a
> particular implementation
>
> sys.implementation.metadata would then give a home for information
> that needs to be builtin, without having to pollute the main sys
> namespace.

I really like this approach, particularly the separation aspect.
Presumably sys.implementation would be more struct-like (static-ish,
dotted-access namespace).  I'll give it a day or two to stew and if it
still seems like a good idea I'll weave it into the PEP.

One question though: having it be iterable (a la structseq or
namedtuple) doesn't seem to be a good fit, but does it matter?
Likewise with mutability.  Thoughts?

-eric