Set up auto-formatting of Python about oil

[andychu]

The code is in the Google Python style, which is basically pep8 with 2 space indents and CapWords for function and method names. All the contributions will have to be in that style going forward, at least until the point where there's a significant amount of code not coming from me.

I changed this bug to be to set up auto-formatting. I have experimented with yapf but didn't apply it to all the code yet. I do want there to be a consistent style and for contributors to not have to worry about reformatting their code.

When the C++ code lands it will use clang-format as well.

[andychu]

Now running flake8, thanks @cclauss. It doesn't auto-format but it catches significant errors.

I'm still somewhat interested in yapf, but it's not a big priority.

[asokoloski]

@andychu Hiya, I looked around for an Emacs mode for Google's python style, and couldn't find one anywhere. This seems to be the canonical source: https://github.com/google/styleguide

Based on that, it looks like Google doesn't use 2-space indentation for python anymore -- so they recommend using the default Emacs python mode style now. I don't know if that's enough reason to change the oilshell project style.

Assuming it's not, are you aware offhand of any Emacs mode files floating around for Google's old python style?

[andychu]

Sorry I'm not sure, I'm a vim user :-)

I will say that I accept any PR that passes tests :) The functionality is the more important part.

I may go back and update the style with subsequent commits. Or if there are consistent contributors then we can automate things more.

Right now flake8 runs in Travis, and I keep it green. It could be made more strict in the future.

[andychu]

Also this issue keeps getting closed because I type #1 in other contexts!

I'm reopening it although there a lot of other things that I think would benefit contributors more, e.g.

https://oilshell.zulipchat.com/#narrow/stream/121539-oil-dev/topic/Dev.20Dependencies.20Problem

[asokoloski]

Ok, thanks, no worries. I just didn't want to make a mess once I figure out a good way to contribute, but I'm sure I'll manage.

[cclauss]

The Python Software Foundation is proposing the canonical way to format Python code and it is called black. It has integrations to Emacs, Vim, other editors. pre-commit hooks, and CI systems. Let's follow Google's lead for the formatting of Go code with gofmt but let's follow the PSF's lead for the formatting of Python code.

[andychu]

test/lint.sh format-oil does this for C++

[cclauss]

Oil bundles legacy Python which went end-of-life on 1/1/2020.
The black formatting tool for Python code will not run on Python 2.

[andychu]

Black can be installed by running pip install black. It requires Python 3.6.0+ to run but you can reformat Python 2 code with it, too.

https://pypi.org/project/black/

In any case this is a moot point until people who have contributed patches want it . It could be black or something else they prefer