Yeah that part is awkward. If you claim source code is Py2 and Py3 compatible (regardless of deps), the correct thing to do is run Flake8 w/ both constraints. Rn, only way to do that is create two targets over the same source file but w/ different constraints. In Twitter, this was the

python23_library

macro. It works, but breaks dep inference due to ambiguity In contrast, w/ tests—which do care about transitive deps—the whole transitive closure must be Py2 and Py3 compatible if you want to test w/ both interpreters