I think for someone with a basic knowledge of both languages, the Ruby version is more understandable than the Python. It's a combination of basic Ruby features, whereas Python's `match` statement is much more obscure - it isn't really Python at all, it's "a DSL contrived to look like Python [...] but with very different semantics" [0].

I don't particularly love the Ruby code either, though - I think the ideal implementation would be something like:

    fn stringify(item) =>
        item.is_a(Interpolation) then
            item.value.convert(item.conversion).format(item.format_spec)
        else item.to_string()

    fn f(template) => template.map(stringify).join()