[GRASS-dev] Moving to Black for Python formatting

Vaclav Petras wenzeslaus at gmail.com
Thu Feb 25 21:00:26 PST 2021

Dear all,

Black is now applied to all except for GUI code (that will change hopefully
soon). There are few exceptions in place, most notably ctypes. The
compliance is checked using Checks in each PR (aka GitHub Actions). The
version used is Black 20.8b1. It will be updated as new releases come with
possibly small changes to the formatting of the code.

Use the same Black version locally, but if you don't, the worst thing which
will happen is that the check will fail and you will need to fix your PR.
There is a new file in the root of the repo called pyproject.toml which
your local Black and perhaps your editor should pick up currently with
settings only for Black. Obviously, the idea is that you just throw Black
formatter at your file and don't care about formatting things manually

A lot happened with Flake8 compiace, but that's mostly irrelevant to Black
except that bulk of formatting issues are gone which are now all enabled
except line length check and one issue which conflicts with Black. This is
accompanied by supporting # % and not just #% in the option parser. Thanks
to this and recent Flake8-related fixes by Anna, it is possible to use
Flake8 quite effectively to check for problems although a lot of issues
still need to be ignored which is configured separately in each major
directory containing Python code.

Several non-whitespace changes were included in the Black formatting,
namely updates of remaining u-string literals to Python 3 and some trailing
comma syntax which now makes Python 3.6 the minimum.

There is also a PR #1391 which will make it easy to ignore these (and
other) formatting commits when doing git blame in the command line. The
GitHub web interface offers an easy way to move over a revision.

All this applies to core repo, not the grass-addons repo. Ideas and
volunteers are welcome.



On Wed, Feb 17, 2021 at 4:03 PM Vaclav Petras <wenzeslaus at gmail.com> wrote:

> Dear all,
> At this moment, we don't use an automatic formatter for Python code and we
> have only limited enforcement of basic formatting rules. This is changing
> as we are moving towards PEP8 formatting compliance and automatic Flake8
> checks.
> We need an automatic formatter and enforcement in the CI. There seems to
> be a clear candidate for that and that is Black (The uncompromising code
> formatter) which was already suggested in 2019:
> https://lists.osgeo.org/pipermail/grass-dev/2019-May/092654.html
> See details about how that applies to GRASS here:
> https://github.com/OSGeo/grass/issues/543
> Here is a first PR (ready to be merged) which makes changes to content of
> scripts and adds a automatic check:
> https://github.com/OSGeo/grass/pull/1347
> Best,
> Vaclav
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