Use | operator for Union traits

[corranwebster]

Following PEP 604 which allows constructs like int | float as a replacement for Union[int, float] should we allow Int | Float as an (optional) replacement for Union(Int, Float)?

The good:

• meaning is fairly clear
• alignment with Python typing

The bad:

• if you want metadata then you'd have to do something like (Int | Float)(foo='bar') which is not very clear compared to Union(Int, Float, foo='bar')

The ugly:

• Int | Float or Int() | Float()? It may have to be the latter, but presumably Python is going to grow some hook for | for types with this change, the same way it did for getitem.

[thedrow]

Note that PEP 593 allows you to annotate annotations with metadata.