On Fri, Aug 30, 2019 at 5:46 AM Andrew Barnert via Python-ideas
<python-ideas@python.org> wrote:
>
> 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.
>
How does that break backward compat?
ChrisA
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