redbaron

Funny, I actually did the same thing for python years ago and also talked about "Lossless Syntax Tree" then start calling it a Full Syntax Tree since CST doesn't really fit; I wasn't aware of the existence of lib2to3 at that time. My goal was different than your: I wanted make writing custom refactoring code (that's it: code that modify source code) and code that works on source code a do-able task. I end up doing some design decisions that I haven't found elsewhere (but this field is hard to explore): - producing json, because datastructure doesn't lie to you and potential interoperability - nodes are responsible for the formatting within itself, in opposition with lib2to3 where a node is responsible for the formatting before itself (or after, I'm not sure anymore) - the tree is design for the human brain instead of an interpreter/compil

There's redbaron, which provides a full syntax tree, and is designed for making such changes: https://github.com/PyCQA/redbaron

It also helps if you want to write code conversion tools, like gofix. I once stopped writing such a tool for a Python project because it was a pain trying to change only the affected lines, while keeping the idiosyncratic syntax of the rest of the files unaffected. (By the way, for people trying to do the same, I recommend the redbaron library, which makes it much easier to handle: https://github.com/PyCQA/redbaron)