Mypy, Pytype, Pyright, and Pyre can help you keep your type-hinted Python code bug-free. Let’s see what each of these useful tools has to offer.

Pyrefly is not the first Python type-checking tool from Meta. Previously, the company delivered Pyre, written in OCaml. Pyre has since been retired; Pyrefly, written from scratch in Rust, replaces it.

I've grabbed Sequence from the typing module, which includes all three Python sequence types—strings, lists and tuples. Once I do that, all of the mypy problems disappear, because all of the arguments ...