On Aug 29, 2019, at 12:09, Dominik Vilsmeier <dominik.vilsme...@gmx.de> wrote:
>
> What about using `(int, str)` for indicating a `Union`? This doesn't have
> compatibility issues and it's similar to `isinstance(foo, (int, str))`, so it
> should be fairly intuitive:
>
> def bar(foo: (int, str) = 0):
> ...
In most languages with similar-ish type syntax, (int, str) means Tuple[int,
str], not Union[int, str]. Scala and TypeScript copied this from ML just like
Haskell and F# did. And I’d bet this is the main reason that {str, int} rather
than (str, int) was proposed the first time around.
But, balanced against the long-standing Python-specific use of tuples for small
numbers of alternatives, including alternative types in places like isinstance,
except, etc.? Maybe that beats the cross-linguistic issue.
Either one seems a lot better than breaking backward compatibility by adding
new operator methods to the type type.
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