Type Checker Comparison¶
Mypy¶
Mypy is a powerful and well-maintained type checker, but it can be a bit slow in practice. I created Zuban with the goal of replacing both Mypy and Jedi with a single, consistent tool.
Zuban strives for a high level of compatibility with Mypy, and in most cases,
you can use zmypy as a drop-in replacement for the mypy command-line tool.
Mypy is in terms of correctness still the best type checker in the Python
universe. The conformance tests show that there are some issues, but these are
mostly minor. Mypy has a lot of upsides over Pyright that are less known. Mypy
for example infers list.append().
Pyright¶
Zuban’s default mode is very similar to Pyright. However, Zuban offers significantly better performance - running faster and using substantially less memory than Pyright.
Pyright has very few bugs and is an all around really solid tool. Pyright has limitations that Mypy does not. A notable example is that Pyright assigns Any in cases of circular references, which can silently result in untyped code. It also skips certain checks in loops by design, missing true positives.
Ty¶
Ty is still lacking a lot of fundamental type system features and is therefore not tracket yet on the conformance test. Ty - like Zuban - is very fast and is doing really well with big code bases. I would personally not recommend using Ty until they pass big parts of the conformance tests. It might become a good tool, but currently lacks many fundamental checks.
Pyrefly¶
Pyrefly has been making big progress with passing conformance tests. It is slightly slower than Ty and Zuban, but is still really fast and has been getting closer to Pylance’s feature set. The biggest drawback is probably its file based invalidation, which can make LSP usage really slow in some cases in big codebases.
Jedi¶
Jedi is not a type checker, but it provides high-quality — albeit relatively slow — autocompletion, go-to-definition, rename, and other basic IDE features. Unlike the other tools listed, it does not perform static type checking.
The slow performance of Jedi was the main reason why I decided to start building Zuban.
