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Re: Pinning dependencies for Apache Airflow

> releases in pip should have stable (pinned deps)
I think that's an issue. When setup.py (the only reqs that setuptools/pip
knows about) is restrictive, there's no way to change that in your
environment, install will just fail if you deviate (are there any
hacks/solutions around that that I don't know about???). For example if you
want a specific version of pandas in your env, and Airflow's setup.py has
another version of pandas pinned, you're out of luck. I think the only way
is to fork and make you own build at that point as you cannot alter
setup.py once it's installed. On the other hand, when a version range is
specified in setup.py, you're free to pin using your own reqs.txt within
the specified version range.

I think pinning in setup.py is just not viable. setup.py should have
version ranges based semantic versioning expectations. (lib>=1.1.2,
<2.0.0). Personally I think we should always have 2 bounds based on either
1-semantic versioning major release, or 2- a lower version than prescribed
by semver that we know breaks backwards compatibility features we require.

I think we have consensus around something like pip-tools to generate a
"deterministic" `requirements.txt`. A caveat is we may need 2:
requirements.txt and requirements3.txt for Python 3 as some package
versions can be flagged as only py2 or only py3.


On Fri, Oct 19, 2018 at 1:47 AM Jarek Potiuk <Jarek.Potiuk@xxxxxxxxxxx>

> I think i might have a proposal that could be acceptable by everyone in the
> discussion (hopefully :) ).  Let me summarise what I am leaning towards
> now:
> I think we can have a solution where it will be relatively easy to keep
> both "open" and "fixed" requirements (open in setup.py, fixed in
> requirements.txt). Possibly we can use pip-tools or poetry (including using
> of the poetry-setup <https://github.com/orsinium/poetry-setup> which seem
> to be able to generate setup.py/constraints.txt/requirements.txt from
> poetry setup). Poetry is still "new" so it might not work, then we can try
> to get similar approach with pip-tools or our own custom solution. Here are
> the basic assumptions:
>    - we can leave master with "open" requirements which makes it
>    potentially unstable with potential conflicting dependencies. We will
> also
>    document how to generate stable set of requirements (hopefully
>    automatically) and a way how to install from master using those. *This
>    addresses needs of people using master for active development with
> latest
>    libraries.*
>    - releases in pip should have stable (pinned deps). Upgrading pinned
>    releases to latest "working" stable set should be part of the release
>    process (possibly automated with poetry). We can try it out and decide
> if
>    we want to pin only direct dependencies or also the transitive ones (I
>    think including transitive dependencies is a bit more stable). *This way
>    we keep long-term "install-ability" of releases and make job of release
>    maintainer easier*.
>    - CI builds will use the stable dependencies from requirements.txt.
> *This
>    way we keep CI from dependency-triggered failures.*
>    - we add documentation on how to use pip --constraints mechanism by
>    anyone who would like to use airflow from PIP rather than sources, but
>    would like also to use other (up- or down- graded) versions of specific
>    dependencies. *This way we let active developers to work with airflow
>    and more recent/or older releases.*
> If we can have general consensus that we should try it, I might try to find
> some time next week to do some "real work". Rather than implement it and
> make a pull request immediately, I think of a Proof Of Concept branch
> showing how it would work (with some artificial going back to older
> versions of requirements). I thought about pre-flaskappbuilder upgrade in
> one commit and update to post-flaskappbuilder upgrade in second, explaining
> the steps I've done to get to it. That would be much better for the
> community to discuss if that's the right approach.
> Does it sound good ?
> J.
> On Wed, Oct 17, 2018 at 2:21 AM Daniel (Daniel Lamblin) [BDP - Seoul] <
> lamblin@xxxxxxxxxxx> wrote:
> > On 10/17/18, 12:24 AM, "William Pursell" <williamp@xxxxxxxxx.INVALID>
> > wrote:
> >
> >     I'm jumping in a bit late here, and perhaps have missed some of the
> >     discussion, but I haven't seen any mention of the fact that pinning
> >     versions in setup.py isn't going to solve the problem.  Perhaps it's
> >     my lack of experience with pip, but currently pip doesn't provide any
> >     guarantee that the version of a dependency specified in setup.py will
> >     be the version that winds up being installed.  Is this a known issue
> >     that is being intentionally ignored because it's hard (and out of
> >     scope) to solve?  I agree that versions should be pinned in setup.py
> >     for stable releases, but I think we need to be aware that this won't
> >     solve the problem.
> >
> > So the problem is going to be stubborn for the rare user not installing
> > into a clean venv, vm, or docker image, or who is not relying on pypi to
> > host the dependencies unmodified.
> > https://pip.pypa.io/en/stable/user_guide/#pinned-version-numbers
> > That doesn't mean it doesn't fix it for the vast majority of users who
> are
> > trying to install a particular supported stable release. Given that
> 1.10.0
> > is the absolute very latest release, it should be supported.
> >
> > Shouldn’t there be an expectation that installing on a clean system from
> a
> > supported stable branch will create a stable installation that can run
> the
> > release?
> >
> >
> >
> --
> *Jarek Potiuk, Principal Software Engineer*
> Mobile: +48 660 796 129