+1
On 09/07/2018 01:09 AM, Simon Baatz 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/631031e38270c5c7c2b2289ff4ab87a058447c5e/plugin/pulpcore/plugin/stages/content_unit_stages.py#L47-L59
[1]
https://github.com/pulp/pulp/blob/631031e38270c5c7c2b2289ff4ab87a058447c5e/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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