Indeed! I also would suggest people to use a CST implementation (parso / LibCST) instead of refactor if they intend do large scale refactors, but from what I can see in my previous attempts (e.g teyit, a unittest assertion formatter) when you deal with small code fragments (a single expression, or a small statement) then you generally don't need to worry much about the style. The only concern is the literals (especially strings, which there are a few different variations of the same AST) where you could resurrect them back from the token stream (which the CustomUnparser representative in refactor allows).

The real start point for this project was to find / replace all type(<literal>)'s in CPython codebase with type(type(<literal>)) (e.g type('') would become type(str)) which is very light weight transformation, and I was able to write a script which did it without having any major problems about style on over 2000 files. Here it is for the reference: https://github.com/isidentical/refactor/blob/master/examples...

Also one thing to note here is that; in the last couple of years, thanks to black (and yapf), the adoptance of code formatters have really increased which is very nice for custom refactoring tools like refactor since the end-code would be refactored anyways so that means if you convert a multi line call, or a list to a single line version then the formatter you use probably reformat that segment anyways.

But thanks for authoring Bowler! It is a very cool project.