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] 
> <javascript:>> 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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