[Python-Dev] Proposal for new 2to23 tool

[Steve Holden]

Collin Winter wrote:
> On Nov 12, 2007 12:50 AM, Graham Horler <graham.horler at gmail.com> wrote:
>> On 12 Nov 2007, 03:24:34, Jan Claeys wrote:
>>> Op zondag 11-11-2007 om 17:19 uur [tijdzone -0800], schreef Brett
>>> Cannon:
>>>> On Nov 11, 2007 4:00 PM, Graham Horler <graham.horler at gmail.com> wrote:
>>>>> I have been developing in Python since 1.5, and now have to support 2.1
>>>>> as a minimum version.  I do like to keep my code runnable on newer
>>>>> versions however, and am considering the feasability of forward
>>>>> compatibility with Python 3.0.
>>>>>
>>>>> I also notice the Leo[1] project could use some assistance with forward
>>>>> compatibility.
>>>>>
>>>>> So I was wondering if anyone else had a need for a 2to23.py tool to help
>>>>> make code compatible with 3.0 but not break it for 2.x.
>>>> What exactly are you proposing?  We already have 2to3
>>>> (http://svn.python.org/view/sandbox/trunk/2to3/) for source-to-source
>>>> translation from 2.x to 3.0.
>>> Graham wants to convert his code such that it works on both Python 2.x
>>> (probably even early versions of it?) & Python 3.x.  Not 2 instances of
>>> code, but one source that works on both 2.x and 3.x...
>> Absolutely
> 
> I don't believe that's possible. There are enough key differences
> between the two that having the same body of code work in both 2.x and
> 3.x would require an extensive, complicated runtime support system
> that no-one has all(the ability, the time, the motivation) to
> implement. And of course, even if you had such a system, the generated
> code wouldn't look anything like well-formed Python and would be a
> maintenance nightmare.
> 
Besides which, the migration path is already well-specified: write in 
3.x-compatible 2.6 and use 2to3 to migrate the code with no further 
processing. This does eventually give you a single code base. Earlier 
versions need not apply - there is no way to accommodate them.

regards
  Steve
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