[Mehdi2277]

I’ve heavily used both mypy/pyright.

The semantic differences are mainly in areas where type system is not specific enough on exact behavior expected. As an example if you have a function that has overloads how do you decide which overload to pick? Sometimes that can become ambiguous especially when type variables are involved or multiple overloads match. Cases like that are where you see most intentional differences and as a user of both type checkers I consider depending on specific behavior there to be like using c++ compiler’s undefined behavior.

The bigger area I see differences is feature development/bug fix velocity. Mypy is maintained well. Pyright is maintained magically and I’ve reported bugs that maintainer fixes the same day. Most bug reports to pyright get fixed in a week. Only a couple tend to stay open for a while. New type system features (peps) get implemented really fast in pyright and usually if you try to use very recent features you will need to wait a while for mypy to catch up. A good example is release time for paramspecs or typevartuple. Most of the time new type system peps are added in pyright while still in draft stage.

[Recursing]

An important difference is that pyright doesn't support plug-ins.

https://github.com/microsoft/pyright/issues/607

E.g. https://github.com/Shoobx/mypy-zope can't work with pyright

[samwillis]

After quickly skimming that issue thread I think the Pyright devs have a very compelling argument not to add a plug-in system. It would encourage none standard behaviour, when really the type system should be capable of describing all behaviour. I think it may be another plus for it.