Would we be able to get rid oftyping._make_union, and just haveTypeVar etc. callUnionType.__class_getitem__ directly?

Would we be able to get rid oftyping._make_union, and just haveTypeVar etc. callUnionType.__class_getitem__ directly?

Yes

Instead of deletingtyping.Union completely, addingUnionType.__class_getitem__, and makingtyping.Union an alias fortypes.UnionType, I wonder if we could just changetyping.Union so that it's a special form that just returns instances ofUnionType:

fromoperatorimportor_fromfunctoolsimportreduce@_SpecialFormdefUnion(self,parameters):returnreduce(or_,parameters)

That would avoid the issue of "Should we renametypes.UnionType to beUnion", as we'd keep them as distinct objects.

But I know your plan is to deal with handling forward refs in| expressions later, which would mean that^ idea above wouldn't work right now (unions involving forward references would break).

So perhaps you could instead expose a_secret_undocumented_constructor method fortypes.UnionType (we can bikeshed over the name), and then just do

@_SpecialFormdefUnion(self,parameters):returntypes.UnionType._secret_undocumented_constructor(parameters)

Or we could just expose the constructor oftypes.UnionType, of course.

Also you can now get rid of this function as part of this PR; prior callers of the function can now just useisinstance() checks againsttypes.UnionType:

That would avoid the issue of "Should we renametypes.UnionType to beUnion", as we'd keep them as distinct objects.

I'd rather not keep them as distinct objects, though; that means we still have two objects that to a user look like the same thing. Plus, we'd haveget_origin(Union[int, str]) != Union.

I guess one of my reservations here is thatUnionType ends up looking like apretty weird type. You can't construct instances of it directly:

>>>from typesimport UnionType>>> UnionType(int,str)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: cannot create 'types.UnionType' instances

...Except wait, you can, we now have a "secret__class_getitem__ backdoor" to create instances directly:

>>> UnionType[int,str,bytes]int | str | bytes

It's very unusual for__class_getitem__ to just directly return instances of the class, and it feelsreally weird to make that theonly way you're allowed to construct instances of the class.

Maybe that means we should just expose the constructor as well as adding__class_getitem__...?

Plus, we'd haveget_origin(Union[int, str]) != Union.

Good point, that would indeed be confusing.

I can make the constructor work. Should it take *args and union them all together?

I can make the constructor work. Should it take *args and union them all together?

That makes sense to me!

It's been long enough, I'm planning to merge this once the tests pass again.

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This PR causes a potential regression:#131933.