[Python-Dev] [Python-3000] Warning for 2.6 and greater

[Anthony Baxter]

On Friday 12 January 2007 21:42, glyph at divmod.com wrote:
> If the plan is to provide a smooth transition, it would help a
> lot to have this plan of foward and backward compatibility
> documented somewhere very public.  It's hard to find information
> on Py3K right now, even if you know your way around the universe
> of PEPs.

I'd like to see this happen, too - however, there's no way I can 
even think about it until after LCA next week. First of all, of 
course, we need to get agreement on the preferred way forward.

> FWIW, I also agree with James that Python 3 shouldn't even be
> released until the 2.x series has reached parity with its feature
> set.  However, if there's continuity in the version numbers
> instead of the release dates, I can at least explain to Twisted
> users that we will _pretend_ they are released in the order of
> their versions.

I'm not sure what "parity with it's feature set" means. I think 
there's going to be some 3.0isms that just cannot be done sanely in 
2.x - for instance, the new I/O subsystem. But I do hope that it's 
_possible_ to work in a version of the language that works in both 
2.6+ and 3.0+, even if under the hood there are differences. For 
instance, if we did "except foo as bar" for 2.6, it might not 
auto-clean-up the exception object when it drops out of the except: 
block. 

I put up www.python.org/sf/1633807 a short time ago that deals with 
one of the big concerns I had - print vs print() (it was also as a 
learning exercise to figure out if it was possible, and how it 
might work). Something similar could probably be done for exec(). I 
suspect the problem cases are going to be things like the 
dictionary code - your idea (in another email) of trying to look up 
globals would probably cause a horrible performance issue, but it 
may be possible to do _something_ clever. 

Anthony
-- 
Anthony Baxter     <anthony at interlink.com.au>
It's never too late to have a happy childhood.