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

[Barry Warsaw]

On Apr 27, 2012, at 12:36 AM, Eric Snow wrote:

>I've written up a PEP for the sys.implementation idea.  Feedback is welcome!

Thanks for working on this PEP, Eric!

>``sys.implementation`` is a dictionary, as opposed to any form of "named"
>tuple (a la ``sys.version_info``).  This is partly because it doesn't
>have meaning as a sequence, and partly because it's a potentially more
>variable data structure.

I agree that sequence semantics are meaningless here.  Presumably, a
dictionary is proposed because this

    cache_tag = sys.implementation.get('cache_tag')

is nicer than

    cache_tag = getattr(sys.implementation, 'cache_tag', None)

OTOH, maybe we need a nameddict type!

>repository
>   the implementation's repository URL.

What does this mean?  Oh, I think you mean the URL for the VCS used to develop
this version of the implementation.  Maybe vcs_url (and even then there could
be alternative blessed mirrors in other vcs's).  A Debian analog are the Vcs-*
header (e.g. Vcs-Git, Vcs-Bzr, etc.).

>repository_revision
>   the revision identifier for the implementation.

I'm not sure what this is.  Is it like the hexgoo you see in the banner of a
from-source build that identifies the revision used to build this interpreter?
Is this key a replacement for that?

>build_toolchain
>   identifies the tools used to build the interpreter.

As a tuple of free-form strings?

>url (or website)
>   the URL of the implementation's site.

Maybe 'homepage' (another Debian analog).


>site_prefix
>   the preferred site prefix for this implementation.
>
>runtime
>   the run-time environment in which the interpreter is running.

I'm not sure what this means either. ;)

>gc_type
>   the type of garbage collection used.

Another free-form string?  What would be the values say, for CPython and
Jython?

>Version Format
>--------------
>
>XXX same as sys.version_info?

Why not? :)  It might be useful also to have something similar to
sys.hexversion, which I often find convenient.

>* What are the long-term objectives for sys.implementation?
>
>  - pull in implementation detail from the main sys namespace and
>    elsewhere (PEP 3137 lite).

That's where this seems to be leaning.  Even if it's a good idea, I bet it
will be a long time before the old sys names can be removed.

>* Alternatives to the approach dictated by this PEP?
>
>* ``sys.implementation`` as a proper namespace rather than a dict.  It
>  would be it's own module or an instance of a concrete class.

Which might make sense, as would perhaps a top-level `implementation` module.
IOW, why situate it in sys?

>The implementatation of this PEP is covered in `issue 14673`_.

s/implementatation/implementation

Nicely done!  Let's see how those placeholders shake out.

Cheers,
-Barry

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