Add support for autoformatting using yapf

[algmyr]

I have my personal ideological issues with Black's opinionated formatting, so I made the small necessary change to add support for yapf as a formatter. I'm all for having many options for this. :)

Thankfully the option was already general enough that the addition was very simple, so good design work there!

[algmyr]

I suspect the formatting check is a false positive? Using single quotes matches the existing code.

[bollwyvl]

I suspect the formatting check is a false positive?

darken's is set up such that all new changes do conform to this repo's target of conforming to a stock black configuration... in this case, double quotes.

ideally, we'd have a bot that just applied these changes, rather than breaking the build: i suppose.

[algmyr]

darken's is set up such that all new changes do conform to this repo's target of conforming to a stock black configuration... in this case, double quotes.

ideally, we'd have a bot that just applied these changes, rather than breaking the build: i suppose.

So what do you prefer? Make darken happy but be inconsistent or make darken sad but be consistent? My own 2c would be to keep it consistent and the quote style change can be done at a later stage in some larger scale refactoring.

[bollwyvl]

says right in the log:

 Changes need auto-formatting. Run:
    darker -r 60625f241f298b5039cb2debc365db38aa7bb522
then commit and push changes to fix.

[algmyr]

darker -r 60625f2

darker is broken locally for me akaihola/darker#264 and I'm not so keen on setting up a venv just for this, I'll just manually fix the one line that it complains about.

[Carreau]

Thanks, sorry about the issue with formatting.