Don't you need to index for `s[:n]`? You need to find the byte position of code point n. In current python this isn't a problem because the strings don't use a

Don't you need to index for `s[:n]`? You need to find the byte position of code point n. In current python this isn't a problem because the strings don't use a variable-width encoding, but we're talking about making Python use utf8 :)