max: comparing int with Decimal doesn't typecheck

[zormit]

from decimal import Decimal

max(1, Decimal(2))

error: Value of type variable "SupportsLessThanT" of "max" cannot be "object"

I would expect this to pass.

[srittau]

We could probably work around this in typeshed for the 2-arity case of max() by using a separate type var for the arguments and returning an union. The base problem is that mypy looks for a common base type in case like this, though, and only finds object. In my opinion it would be preferable to experiment with what happens if mypy would infer a union instead.

[erictraut]

This is arguably a bug / limitation in mypy rather than a problem with the typeshed definition. The problem is that mypy uses a "join" operation to widen types in its type constraint solver rather than using a union operation.

The above sample type checks fine with pyright, which uses unions to widen types in its constraint solver. The return type of the call to max is int | Decimal.

[srittau]

Eric explained it better than me. I don't think we should change the stubs in this case.