[exyi]

Python does not need that, as it has built-in type annotation support. The annotation is any expression, so you can in theory express anything a custom type-only language would allow you (although you could make it less verbose and easier to read).

However, the it IMHO just works much worse than TS because: * many libraries still lack decent annotations * other libraries are impossible to type because of too much dynamic stuff * Python semantics are multiple orders of magnitude more complex than JavaScript. Even just the simplest question: Is `1` allowed in parameter typed `float`? What about numpy float64?

[tl2do]

Thanks for helping me understand. I wasn't aware of Python's type annotation support. I did some quick research and learned that type annotations don't cause compile errors even when there are type errors. Is that why type checkers like Pyrefly exist?

[linsomniac]

Correct, currently in Python the type checking is implemented more in a linting phase than in a compiling or runtime phase. Though you can also get it from editors that do LSP, they'll show you type errors while editing the code.

[tl2do]

Thanks linsomniac and exyi. I didn't realize Python's type hints are checked by linters, not the compiler. Learned something today.

[linsomniac]

I really like them, I'm a very long time Python programmer ('97) and so the ability to just bang something simple out and not care about the typing is nice at times, but for anything very serious at all it's very nice to have the option to add the type annotations and get the bulk of the benefits from it.

[LtWorf]

Yes, but there are also runtime type checkers that can be used to check that input data conforms to the expected types (aka a schema but defined using python types and classes).