The first mistake we're going to see a library developer make is:

    def execute(query: Union[str, Template]):

Maybe because they want their execute function to be backwards compatible, or just because they really do want to allow either raw strings are a template string.

> they really do want to allow either raw strings are a template string.

I’d consider that an invalid use case:

1. You can create a template string without placeholders.

2. Even if the caller does need to pass in a string (because they’re executing from a file, or t-strings don’t support e.g. facetting) then they can just… wrap the string in a template explicitly.