Message 387817 - Python tracker

> @BTaskaya, do you think you'll have time to open a PR with your AST validator this weekend? It looks good to me (assuming tests pass).

Unfortunately not. I believe it still lacks tests for invalid cases, but other than that should work. If you'd like to take it on feel free, if not I'll create a PR next weekend with tests (probably after release, though I believe it is not a blocker as is).