Extremely slow when using Black on large files

[Hubro]

Using Black on a large Python file with Neoformat is extremely slow.

If the contents of the file doesn't require reformatting, :Neoformat black returns "no change necessary" in 3-400 ms, just like black in the command line. However, if I add an extra empty line so the file has to be reformatted, running the same command takes 3-4 full seconds. This is a massive pain to wait for every time I save the file.

Using the official Black plugin instead, reformatting takes pretty much exactly as long as it does when running Black through the command line, i.e. 3-400 ms.

[YuCao16]

Same here

[alecandido]

Something similar is happening also with prettier.

[long2ice]

Same here

[nicolasaunai]

still very slow