[Python-Dev] sys.implementation

Brett Cannon brett at python.org
Wed May 9 16:44:59 CEST 2012

On Wed, May 9, 2012 at 5:57 AM, "Martin v. Löwis" <martin at v.loewis.de>wrote:

> On 27.04.2012 09:34, Eric Snow wrote:
>> On Thu, Apr 26, 2012 at 8:31 AM, Barry Warsaw<barry at python.org>  wrote:
>>> It's somewhat of a corner case, but I think a PEP couldn't hurt.  The
>>> rationale section would be useful, at least.
>>   http://mail.python.org/**pipermail/python-ideas/2012-**
>> April/014954.html<http://mail.python.org/pipermail/python-ideas/2012-April/014954.html>
> Interesting proposal. I have a number of comments:
> - namespace vs. dictionary. Barry was using it in the form
>  sys.implementation.version. I think this is how it should work,
>  yet the PEP says that sys.implementation is a dictionary, which
>  means that you would need to write
>  sys.implementation['version']
>  I think the PEP should be silent on the type of sys.implementation,
>  in particular, it should not mandate that it be a module (else
>  "from sys.implementation import url" ought to work)
>  [Update: it seems this is already reflected in the PEP. I wonder
>   where the requirement for "a new type" comes from. I think making
>   it a module should be conforming, even though probably discouraged
>   for cpython, as it would make people think that they can rely on
>   it being a module.

That stems from people arguing over whether sys.implementation should be a
dict or a tuple, and people going "it shouldn't be a sequence since it
lacks a proper order", but then others saying "it shouldn't be a dict
because it isn't meant to be mutated" (or something since I argued for the
dict). So Eric (I suspect) went with what made sense to him.

> I wish there was a builtin class
>     class record:
>        pass
>   which can be used to create objects which have only attributes
>   and no methods.

I have heard this request now a bazillion times over the years. Why don't
we have such an empty class sitting somewhere in the stdlib with a
constructor classmethod to simply return new instances (and if you want to
get really fancy, optional keyword arguments to update the instance with
the keys/values passed in)? Is it simply because it's just two lines of
Python that *everyone* has replicated at some point?


> Making it a type should also work:
>    class implementation:
>       name = "cpython"
>       version = (3,3,0)
>  in which case it would an instance of an existing type, namely,
>  "type"]
> - under-specified attributes: "run-time environment" doesn't mean much
>  to me - my first guess is that it is the set of environment variables,
>  i.e. a dictionary identical to os.environ. I assume you mean something
>  different ...
>  gc_type is supposedly a string, but I cannot guess what possible
>  values it may have. I also wonder why it's relevant.
> Regards,
> Martin
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