How to raise Error on LiteralString

[randolf-scholz]

This issue come from pandas-stubs.

Is it possible, using LiteralString PEP675, to write an overloaded function foo(x) such that

• foo(x: Literal["a", "b", "c"]) passes
• foo(x: LiteralString) raises a typing error
• foo(x: str) passes

i.e. any non-literal string is ok, but for literal string the type checking acts as a defense against typos.

[erictraut]

No, that's not possible (nor would it make sense given the way that subtyping and overloads work in Python). LiteralString is a subtype of str, so if you provide an overload that accepts a str, it will (by definition) accept a LiteralString. A type checker will emit an error only if the supplied arguments fail to match any of the overloaded signatures.

[randolf-scholz]

So I guess this is another case where one would love to have Intersection and Not, since then Intersection[str, Not[LiteralString]] would be the correct overload.

[Akuli]

A @typing_error decorator would help too: #1043