PyPy is something that I had not really considered. It's not something
I really use myself. I would hope that PyPy would be migrated to be
compatible with a supported version of Python by 2020. I'll see if I
can find out what their roadmap looks like.

Aaron Meurer

On Fri, May 20, 2016 at 1:09 PM, Denis Akhiyarov
<[email protected]> wrote:
> One question - after python 2.7 is dropped which python 3+ versions would be
> supported?
>
> From the chart on that page is looks like only Py 3.5+, which means no PyPy,
> unless they commit to catch up.
>
>
> On Thursday, May 19, 2016 at 11:00:50 AM UTC-5, Aaron Meurer wrote:
>>
>> In case it wasn't clear, I'd like to hear feedback from users of SymPy, as
>> well as from developers.
>>
>> Aaron Meurer
>>
>> On Thu, May 19, 2016 at 11:51 AM, Aaron Meurer <[email protected]> wrote:
>>>
>>> Hi all.
>>>
>>> Some of us in the broader scientific Python community have been
>>> discussing the future of Python 2 support for various libraries. As you may
>>> know, Python 2.7 will cease to be supported by the core Python development
>>> team in 2020, meaning all updates to it will cease, including security
>>> updates. However, even though we are six major versions into Python 3, the
>>> larger community as a whole is still slow on uptake for supporting it.
>>>
>>> The proposal is for libraries to let the community know now when they
>>> plan to drop Python 2.7 support, so that they will better prepared for it,
>>> and hopefully so as an encouragement to start transitioning now, if they
>>> haven't already.
>>>
>>> I propose that we put it on our roadmap to drop Python 2.7 support in
>>> 2019. That is, the first release we do in 2019 will be the last to support
>>> Python 2.7. This is consistent with what we've done so far, which is to drop
>>> support for Python versions once they cease being supported by core Python.
>>>
>>> Other libraries, such as IPython and likely matplotlib, are also joining
>>> together to sign a formal statement about this, which is drafted at
>>> https://python3statement.github.io/.
>>>
>>> Some libraries, such as IPython and matplotlib, are proposing to support
>>> a patchfix branch for an older version that supports Python 2.7, but I am
>>> opposed to any plan for SymPy that means supporting more than one version at
>>> a time, as I don't think we have the development effort for it.
>>>
>>> I would like to hear feedback on this, both positive and negative. It
>>> isn't an official decision yet, until the community agrees on it.
>>>
>>> Here is my rationale for doing this. I also plan to publish a blog post
>>> about this soon, which goes into more detail:
>>>
>>> As you also probably know, SymPy, like other Python libraries, has done
>>> extra work to support Python 2 and 3 in the same codebase. While this work
>>> is easier than it used to be, it does put a maintainence burden on SymPy,
>>> and it prevents us from using language features which are Python 3-only. One
>>> language feature in particular that I would love to be able to use in SymPy
>>> is keyword-only arguments. This lets you write, for instance
>>>
>>> def function(x, y, *, flag=False):
>>>     ...
>>>
>>> and then function(x, y, True) is a TypeError. Only function(x, y,
>>> flag=True) will work. This future-proofs the API, e.g., you can easily
>>> change it to function(x, y, z, *, flag=False) without any API breaks, and it
>>> forces explicitness in keyword arguments. That's one example. There are
>>> other Python 3-only features that we may or may not be able to make use of
>>> as well (like function annotations).
>>>
>>> And even without that, the maintenance burden of supporting both versions
>>> is nontrivial. It means all developers have to know about the quirks of
>>> Python 2 and 3, regardless of which one they use primarily. It means that we
>>> always have to remember to add all the right compatibility imports at the
>>> top of files, and avoid things which are one version-only. And it means
>>> extra builds in the test matrix.
>>>
>>> Aaron Meurer
>>
>>
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