[python-committers] Deprecation Policy PEP

[Steven D'Aprano]

On Tue, Feb 02, 2016 at 09:40:52AM -0500, Barry Warsaw wrote:
> On Feb 02, 2016, at 03:33 PM, Ezio Melotti wrote:
> 
> >Changing the major version should be done for incompatible changes, and just
> >doing it after 3.9 will probably just create confusion for both users that
> >will wonder if it's incompatible with Python 3 and for things like the
> >executable name.  Hopefully we won't need to jump to Python 4 for a long
> >time.
> 
> Changing the major version number is a much bigger political and psychological
> step than just bumping 3 to 4.  I say let's put it off as long as possible,
> and there's nothing wrong with two digit minor versions.

It will break any code that does

    if sys.version < "3.3": ...

for example. Sure, people shouldn't do that, but they will.

Are there any other languages or systems which bumped the major version 
number while keeping language changes relatively minor? I can think of a 
couple of examples of languages which bumped the major version number 
without making big disruptive changes:

* Python 1.5 -> 2.0 (technically there was a 1.6 in there as well, but 
that wasn't used by many people).

Admittedly, fewer people used Python back then, and the version bump 
wasn't following a similiar, but backwards incompatible, version bump.

* PHP 5.x -> 7.0. I count nine feature removals, but none of them look 
big. http://php.net/ChangeLog-7.php

* Java major version bumps are rarely backwards incompatible, as far as 
I can tell. I had a Java developer explain to me that he treats the N 
in "Java N" as effectively a minor release number.


The point being, I'm not entirely sure I agree that a major version bump 
would *necessarily* be considered a big deal, let alone a barrier to 
adoption. It might be nice to have a really big feature added in 4.0 to 
justify the version bump, but I don't think it's a "Must Do". Having 4.0 
being a lightweight evolutionary step up from 3.9 might even reassure 
people that we're back to normal operating practice, without the 
extraordinary 2->3 transition.



-- 
Steve