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Anders Hovmöller
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A quick performance comparison of Python code formatters


We’ve been talking about code formatters for Python at work since we’re using Elm and we’ve been super happy about how code formatting works with elm-format. I tried Black a bit to see how it looks and my initial impression is that I like it (except “ for quotes, what’s up with that?) but it felt slow. So obviously it’s benchmark time!

The three big Python code formatters seem to be yapf, autopep8 and black. From what I understand autopep8 does the least formatting, so we should take its speed with that in mind.

I benchmarked against the code base I work on professionally. It’s 240k dry lines of code, i.e. not counting blank lines or lines that just contain comments.


Score one for Black!

Both yapf and autopep8 have some annoying behaviors:

And the kicker is that Black has a --fast option that skips some internal checks that runs in 48 seconds on this test. That’s pretty much check mate as far as I’m concerned.

Update: I did some digging for another article and it turns out Black cheats a bit here: it runs in parallel. If I turn that off it takes 2.8m on the same benchmark. Still ok though I think.

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