Paul Sokolovsky writes:
That kinda means "string is atomic", instead of your "characters are atomic".
I would be very surprised if a language that behaved that way was called a "Python subset". No indexing, no slicing, no regexps, no .split(), no .startswith(), no sorted() or .sort(), ...!?
If that's not what you mean by "string is atomic", I think you're using very confusing terminology.