[Python-ideas] Smoothing transition to Python 3

[Paul Moore]

On 4 June 2016 at 09:12, Neil Schemenauer <nas-pythonideas at arctrix.com> wrote:
>> As above (and we definitely won't revert it - it's one of the more
>> appreciated changes reported by educators)
>
> I'm not proposing to revert it.  Sometimes I wonder if people
> actually read my proposal.  I want a version of Python between 2.7.x
> and 3.x that allows it with a warning.

Who do you propose develops that version? Will you do so to help the
next group of people in your situation? Even though there has been a
formal pronouncement that Python 2.8 will not happen, someone could
produce a fork, call it "transition Python" and add all the features
you're asking for. Would people use it? I don't know. But the people
who've asked for such a thing in the past have apparently never been
sufficiently convinced it was a worthwhile effort to put their own
time into it.

People with large Python 2 codebases don't have to port. The lack of
ongoing support for Python 2 from the core devs can be handled by
other means (pay your distribution vendor for extended support, accept
that Python 2 will freeze - it's not as if it's going to stop working
- or maintain your own patches for Python 2.7, lots of options).
Which, of course, may or may not suit your needs.

The big part of the equation that's yet to become a major issue is
libraries. At some point, library authors will start to face the
decision of whether maintaining Python 2 support is worth it. Maybe
only once Python 2 is no longer supported by the core devs, I don't
know. But I don't see any major libraries that are *not* supporting
Python 3 (even Twisted, probably the highest-profile example of a
library that's had major problems porting, is getting Python 3
support). So the Python 2 community faces the prospect of what to do
when libraries like pip, requests, numpy, ... stop supporting Python
2. (Equally, it would be a big issue if one of those major libraries
announced that it would no longer support Python 3, but my instinct
says that's unlikely).

So it seems to me that for Python 2 users, the options are:

1. Stay where you are:
   Advantages - no porting costs, no risk of introducing new bugs in the port
   Disadvantages - platform will become less well supported (may cost
money for support), key dependencies may also desupport Python 2,
adding to the support question.
2. Port to Python 3:
   Advantages - Ongoing free support from the Python community,
possibly better or cheaper vendor support
   Disadvantages - Porting cost, possibility of introducing new bugs
during the port.
3. Your proposal of creating a transitional version:
   Advantages - ??? Porting costs are smaller? But there's the cost of
developing the transitional version (or paying someone to do so).
Unless you were hoping someone would do that for free, or you think
that spreading the cost over a lot of people with the same needs will
reduce the cost sufficiently...
   Disadvantages - At the moment, this option doesn't exist. So delays
before you can even use it. And potential users (who might contribute
help to the effort) may not be willing to wait.

Any others? For me the killer there is "porting cost" which is why I
say you don't have to port. The costs may easily outweigh the
benefits. Maybe in your case, they did but nobody realised that in
time. Maybe there's not enough impartial information on how to
quantify the costs. I don't know.

Paul