On Thu, Aug 29, 2019 at 5:56 PM Andrew Barnert via Python-ideas <
[email protected]> wrote:
> I think {int, str}, which someone proposed in one of the earlier
> discussions, is nice. What else would a set of types mean (unless you’re
> doing mathematical type theory rather than programming language typing)?
> But it’s unfortunate that things like isinstance and except take a tuple of
> types (and it has to be a tuple, not any other kind of iterable), so a set
> might be just as confusing for hardcore Python types as a tuple would be
> for polyglots.
>
> If the compatibility issue isn’t a big deal (and I trust Guido that is
> isn’t), I think int | str is the best option. It’a an operator that means
> union, it’s used for sum/union types in other languages, it makes perfect
> sense if you read it as “int or str”… I cant imagine anyone being confused
> or put off by it.
>
I just realized one big advantage of `{int, str}` over `int|str`. It
doesn't require adding anything to `type`, and we don't need to introduce a
new lightweight builtin union type.
We could still do `~int` -- it would just return `{int, None}`. (But that
*would* require adding to `type`.)
If we did this, it would behoove us to support `isinstance(x, {int, str})`
as well. A wrinkle with that: the current code is naively recursive,
because it's impossible to create a loop in a tuple (other than using the C
API). Tuples are also easier to traverse than sets. But those are
surmountable problems.
--
--Guido van Rossum (python.org/~guido)
*Pronouns: he/him/his **(why is my pronoun here?)*
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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