It was considered, but the initial goals of Bowler was to a) build on top of lib2to3 in an attempt to get broader upstream support for maintaining it as an "off

It was considered, but the initial goals of Bowler was to a) build on top of lib2to3 in an attempt to get broader upstream support for maintaining it as an "official" cst module, which fizzled out, and b) to use some of the more complex matching semantics that lib2to3 enabled, which baron and other cst alternatives don't really attempt to cover. Things like "find any function that uses kwargs" or "find any class that defines a method named `bar`" can be easily expressed with lib2to3's matching grammar, and no other CST that I'm aware of (that isn't itself based on lib2to3) has equivalent functionality. This is something we wanted to add to LibCST, but haven't had the time to focus on given other priorities. Meanwhile, we used LibCST to write a safer alternative to isort: https://usort.readthedocs.io https://usort.readthedocs.io