[Python-Dev] draft pep: backwards compatibility

[R. David Murray]

On Fri, 19 Jun 2009 at 14:15, Antoine Pitrou wrote:

> Benjamin Peterson <benjamin <at> python.org> writes:
>>
>> I mean that if you pass X and Y into a function and get Z in 2.6, then
>> you should be able to get Z from passing X and Y in 2.7 even if
>> there's a new argument that returns Z' if you pass True to it.
>
> Well, except if returning Z rather than Z' was a bug.

I'm pretty sure there have been cases of keeping buggy behavior in point
releases for backward compatibility reasons.  I think the decision has
depended on the nature, severity, and age of the bug, and the estimated
likelihood that code in the wild would break if the bug were fixed.

--David