On Sun, Jun 14, 2020 at 8:41 AM Paul Moore
As Chris A says, I'd be inclined to see how far we can get with (extended) type hints before going for new syntax, though.
def foo() -> {1, 2, 3}: return 2
That is, of course, valid syntax right now. I wonder what a type checker could do with it? Similarly,
Well, the thing is that there is no way to know at compile time what Value is getting passed in -- this is really more a way to catch a ValueError than TypeError, so can't be done with static type checking. Unless you do, as ChrisA suggests, crate a Type (and Enum) that you can then check for. But while I like the idea of Enums, particularly for, say multi-valued flags, They require an extra name and extra typingthat I find annoying (annoying enough that I haven't used one yet in my code. That is, I prefer, so use Chris A's example: some_function(1, 2) ... to: from some_module import Spam some_function(Spam(1), 2) ... That being said, if you want your API to be "safe" and type-chackable, then Enum is the way to go. As for the OP, who was asking for a run-time check, if: def fun(a, b): if a not in {1,2,3}: raise ValueError("a has to be one of these values: 1, 2, 3") is too verbose, you can always write a utility function (or a callable class or closure that stores the options) to make it a simple one-liner: def fun(a, b): value_check(a, options= {1, 2, 3}) -CHB -- Christopher Barker, PhD Python Language Consulting - Teaching - Scientific Software Development - Desktop GUI and Web Development - wxPython, numpy, scipy, Cython