[Python-ideas] Create Python 2.8 as a transition step to Python 3.x

[Andrew Barnert]

On Jan 18, 2014, at 17:12, Neil Schemenauer <neil at python.ca> wrote:

> On 2014-01-17, Andrew Barnert wrote:
>> What exactly do you mean by "the bytes/unicode changes"?
> 
> I mean all of those things that you listed.   bytes = the Python 2.7
> str object, str object is Python 2.7 unicode object.

If you really mean I the things I listed, we already have that. It's called Python 3.4. If you want to fork it and rename it 2.8, I can't imagine who that would help.

A smaller list of changes _might_ mean a useful intermediate target, but if you're not even willing to think through the issues and discuss them, you're not going to come up with such a list.


>> I suspect that, whatever your exact answers, it would be a lot
>> easier to fork 3.4 and port the 2.7 behavior you want than to fork
>> 2.7 and backport almost all of 3.4.
> 
> It's a lot of work no matter which way you do it.  That's one of the
> biggest problems with this idea.
> 
>> And if you do it that way, you could even adapt the idea someone
>> proposed a few weeks ago—not popular on this list, but maybe
>> popular with your target audience—of turning each change on and
>> off with a "from __past__ import misfeature" statement, so people
>> could pick and choose the ones they need, and gradually remove
>> past statements as they port from your forked 2.8 to real 3.4.
> 
> You can't make those changes with __future__/__past__ imports.  They
> effect the whole runtime, not single module.

Sure you can. It already works for __future__ Unicode literals in 2.7. Most of the other changes would work just as well. A few might not--but again, you have to go through them one by one and decide.

>> However, I also suspect that, whatever your exact answers, it
>> won't be that useful. Look at people's reasons for not moving to
>> 3.x:
> 
> Imagine I'm a developer with the Python 2.x codebase.  I'm either
> lazy or I'm too busy with other company projects that I can't put
> the effort into porting my 2.x code to 3.x, even if all the 3rd
> party libraries have been ported.
> 
> How can we make it easier for them to move their code towards Python
> 3.x rather than keeping it as 2.x?  

Not by publishing something that requires the exact same code changes as 3.4 and calling it 2.8. That might trick a handful of devs, and help a handful of others trick their managers, but that's not much benefit.

> A maintained interpreter to run
> Python 2.x code is going to continue to exist.  Some python-dev
> people seem to suggest we can suggest that end of maintenance of
> Python 2.7 is going to force people to port their code.  That's
> ridiculous.

I've never heard anyone suggest this. The people who are most gung ho about 3.x are the ones who keep pointing out that many apps never need to port and that people like RedHat are likely to continue supporting 2.7 long after the PSF stops doing so.

> I want to make it more attractive for these developers to move
> towards Python 3 rather than stalling out on Python 2.7 forever.
> How best to do that is still to be determined.  I think my 2.8 idea
> might be better than the status quo but it's just a crazy idea.

A crazy idea is one thing; a misinformed idea is another.
> 
>> I'm having a hard time imagining code that would be easy to port to 2.8, but not to 3.x. For example:
>> 
>>     payload = <some object with a __str__ method to serialize it>
>>     sock.sendall('Header: {}\r\nAnother: {}\r\n\r\n{}'.format(
>>         headers['header'], headers['another'], payload))
>> 
>> Even with just the two changes you already suggested: First, you
>> have to change the literal to a bytes literal.
> 
> That part is easy, could even be done with an automated tool
> (change u' to ' and ' to b').
> 
>> More seriously, you have to rename that payload type's __str__
>> method to __bytes__.
> 
> Nope, no __bytes__ in my proposed 2.8.

Then the code just doesn't work. The payload types existing __str__ returns a bytes object, which raises a TypeError.

>> And if it does any string stuff internally, like encoding JSON,
>> that has to change. Meanwhile, your logging code probably relies
>> on the same _str__ method actually returning a str, so you have to
>> add one of those. Assuming headers is a dict of strs, you either
>> need to go back up the chain (or into the API that provides it)
>> and change that so it's been a dict of bytes all along, or you
>> need to explicitly encode the headers here. That doesn't sound too
>> hard overall… but that gives you working Python 3.5 code (assuming
>> PEP 460 goes through). And there doesn't seem to be any shortcut
>> that would give you working 2.8 code without also working in 3.5.
> 
> I think you are misunderstanding my proposal, no problems like the
> ones you suggest, bytes() would be the Python 2.7 str class.  All
> the internal bytes/unicode internals would be like 2.7.

You're contradicting yourself. You explicitly said that your proposal includes all of the changes I suggested. That includes, right near the very top, things like no automatic str/bytes conversions. But you seem to be assuming they would still exist even though you decided to remove them.

> That's
> basically the whole idea of this proposal, the bytes/str change in
> 3.x is the really disruptive one, separate it into separate
> interpreter versions 

But you've proposed that the all of the elements of the str/bytes change should be part of 2.8, which means it will be just as disruptive as 3.4.