Stop writing Python 4 incompatible code

[Terry Reedy]

On 1/13/2016 7:10 PM, Steven D'Aprano wrote:
> On Thu, 14 Jan 2016 03:25 am, Random832 wrote:
>
>> On Wed, Jan 13, 2016, at 09:21, sjmsoft at gmail.com wrote:
>>> This strikes me as very good advice.  Thanks for being so far-sighted.
>>> And let's hope that Python 4 has fewer incompatibilities (none would
>>> good) than Python 3!
>>
>> Who says there's going to be a Python 4? I always assumed 3.9 would be
>> followed by 3.10.
>
>
> Guido has a *very* strong dislike for two digit minor version numbers. It
> took a fair amount of arm-twisting to get him to accept two digit micro
> version numbers, like 2.7.10. It is doubtful that we'll see 3.10.
>
> But he has definitely ruled that 4.0 (assuming there is one) will not be a
> major backwards-incompatible version like 3.0 was.
>
> That's not to say that there won't be any backwards incompatibilities at
> all, but they will be relatively minor, like the change from 2.5 to 2.6. (I
> bet most people don't even know that 2.6 broke backwards-compatibility.)

There are a number of deprecations that will not be turned into removals 
while 2.7 remains on support but which probably will be removed after, 
and after they have been giving DeprecationWarnings for at least 2 3.x 
releases.  So code that does not have deprecated features will not be 
affected.

This should be after 3.8.  If removals happen in a release that would be 
'3.9', I expect that it would be '4.0' instead.  (But there is no 
definite plan and will not be until the time comes.

-- 
Terry Jan Reedy