[Python-Dev] a new type for sys.implementation

[Mark Shannon]

Nick Coghlan wrote:
> On Fri, Jun 1, 2012 at 9:49 PM, Mark Shannon <mark at hotpy.org> wrote:
>> What is wrong with something like the following (for CPython)?
>>
>> class SysImplemention:
>>    "Define __repr__(), etc here "
>>    ...
>>
>> sys.implementation = SysImplemention()
>> sys.implementation.name = 'cpython'
>> sys.implementation.version = (3, 3, 0, 'alpha', 4)
>> sys.implementation.hexversion = 0x30300a4
>> sys.implementation.cache_tag = 'cpython-33'
> 
> Because now you're double keying data in a completely unnecessary
> fashion. The sys module initialisation code already has access to the
> info needed to fill out sys.implementation correctly, moving that code
> somewhere else purely for the sake of getting to write it in Python
> instead of C would be foolish. Some things are best written in Python,
> some make sense to write in the underlying implementation language.
> This is one of the latter because it's all about implementation
> details.

Previously you said that "it needs to handled in the implementation 
language, and explicitly *not* in Python".
I asked why that was.

Now you seem to be suggesting that Python code would break the DRY rule,
but the C code would not. If the C code can avoid duplication, then so
can the Python code, as follows:

class SysImplementation:
     "Define __repr__(), etc here "
     ...

import imp
tag = imp.get_tag()

sys.implementation = SysImplementation()
sys.implementation.name = tag[:tag.index('-')]
sys.implementation.version = sys.version_info
sys.implementation.hexversion = sys.hexversion
sys.implementation.cache_tag = tag

Cheers,
Mark.