[Pulp-dev] Proposal to drop support of Python 3.5 for Pulp 3

[Daniel Alley]

Personally, +1.  I ran into this issue myself and it was infuriating to
deal with.

dict objects preserve insertion-order (officially declared part of
>   the language with Python 3.7). Eliminates a source of subtle
>   "works on 3.6, sometimes works on 3.5" bugs.
>

Just to expand on this though:

For Ubuntu, it is part of 18.04 LTS. Debian does not have Python 3.6 in
> stable yet.
>

It does mean that we won't be able to support Ubuntu 16.04 (or previous) or
Debian at all until the next release (~May 2019), unless they install a
newer Python themselves.

On Fri, Sep 7, 2018 at 2:09 AM, Simon Baatz <gmbnomis at gmail.com> wrote:

> I had a discussion on IRC with Brian yesterday which led to the
> question whether we can drop support for Python 3.5. I think there are
> good reasons for this, see the rationale below.
>
> Brian proposed to initiate a vote on this topic (and find out whether
> this "community thing" works :-) ).
>
> Please send feedback by Friday Sept 14th. Especially, let me know if
> there are specific reasons for depending on Python 3.5. The
> corresponding issue is 3984 [7].
>
> Cheers,
> Simon
>
>
> Rationale:
>
> The trigger for the discussion was to get rid of boilerplate code like
> this [0], [1] to handle batches in the stages API. This becomes a
> single line [2] when using an asynchronous generator [3]. Adding the
> `batches()` async generator to Pulp core would simplify existing
> stages and ease implementation of stages in plugins.
>
> Async generators have been introduced in Python 3.6. Thus, to make the
> `batches` generator available in the Pulp core plugin API, we either
>
> - have to drop support for Python 3.5 or
>
> - reimplement the async generator as an async iterator (which would be
>   more convoluted but looks doable)
>
>
> I prefer to drop 3.5, since this will allow to use additional language
> features[4]. Among them:
>
> - As said, async generators/async comprehensions. Async generators are
>   simpler to write and understand than async iterators.
>
> - String interpolation "f-Strings" [5]
>
> - dict objects preserve insertion-order (officially declared part of
>   the language with Python 3.7). Eliminates a source of subtle
>   "works on 3.6, sometimes works on 3.5" bugs.
>
> - One version less to support is always a good thing (provided nobody
>   really requires it)
>
> - Type annotations are currently not used by the Pulp project, but if
>   the project decides to use them in the future: IMHO type annotations
>   (which are great btw.) began to feel “right† with 3.6. Working with
>   them in 3.5 can be clumsy at times.
>
> - And of course: [6]
>
>
> Python 3.6 has the OS/distribution support we need:
>
> - Python 3.6 SCL is available for RHEL 7 / CentOS 7
> - It is part of Fedora as of Fedora 26
>
> For Ubuntu, it is part of 18.04 LTS. Debian does not have Python 3.6 in
> stable yet.
>
>
>
> [0] https://github.com/pulp/pulp/blob/631031e38270c5c7c2b2289ff4ab87
> a058447c5e/plugin/pulpcore/plugin/stages/content_unit_stages.py#L47-L59
> [1] https://github.com/pulp/pulp/blob/631031e38270c5c7c2b2289ff4ab87
> a058447c5e/plugin/pulpcore/plugin/stages/artifact_stages.py#L48-L60
> [2] https://github.com/gmbnomis/pulp_cookbook/blob/
> ca4882cecab16995c5713d27131da8112a5f5a0c/pulp_cookbook/app/
> tasks/synchronizing.py#L98
> [3] https://github.com/gmbnomis/pulp_cookbook/blob/
> d44ed593925b78c046e1b568810b15acbdad5ac4/pulp_cookbook/app/
> tasks/synchronizing.py#L26
> [4] https://docs.python.org/3/whatsnew/3.6.html
> [5] https://docs.python.org/3/whatsnew/3.6.html#pep-498-
> formatted-string-literals
> [6] https://twitter.com/raymondh/status/844955415259463681
> [7] https://pulp.plan.io/issues/3984
>
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