On Dec 9, 2011, at 12:43 AM, Guido van Rossum wrote:

> Even if it weren't slow, I still wouldn't use it to automatically
> convert code at install time; a single codebase is easier to reason
> about, and easier to support.  Users send me tracebacks all the time;
> having them match the source is a wonderful thing.
> 
> Even though 2to3 was my idea, I am gradually beginning to appreciate this 
> approach. I skimmed the docs for "six" and liked it.

Actually, maybe I like it a bit better than I thought.

The biggest issue for the single-codebase approach is 'except ... as ...'.  
Peppering one's codebase with calls to sys.exc_info() can be a real performance 
problem, especially on PyPy.  Not to mention how ugly it is.  For some reason I 
thought that this syntax was only supported by 2.7 and up; I see now that it's 
2.6 and up.

This is still a problem for 2.5 support, of course, but 2.6-only may not be too 
far away for many projects; Twisted's support schedule for Python versions 
typically follows Ubuntu's, which means that we might be able to drop 2.5 as 
early as 2013! :).  Even in the plans that involve 2to3 though, "drop 
everything prior to 2.6" was always supposed to be step 0, so "single codebase" 
adds much less of a burden than I thought.

-glyph

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