Fwiw I read Eric's entire proposal (I like it) but totally missed the presence of single, double, triple underscores. Which caused me to be very confused reading Matt De Valle's reply, until I went back and noticed them, and the lightbulb went on. Based on that experience, and also Matt's comment about how people might automatically try to add a second signature directive using the same variable name, I would suggest that maybe it would be preferred, when giving examples in documentation etc, to not use underscores like this as the placeholders.... It is easy to miss that the variable names are required to be different. Different comment: in the other thread I liked the idea of mimicking the syntactical way of writing a function signature (although this might cause other problems): @dataclass class C: # positional only arguments required at top a: Any Pos : '/' # normal only after this line, can't go back b: Any Kwd: '*' # kwd only after this line, can't go back c: Any But as Eric pointed out, there could be a lot of value in being able to go back and forth. I know think his idea is better. BIKE SHED: If switching back and forth does win out, I think we should NOT try to use the characters '/' and '*' to specify the signature directives because they would lead the reader to believe they work the same as in a function signature. Aside from the issue if going back and forth, in Eric's proposal the positional directive comes *before* the positional arguments, rather than after like in a function signature. Since this is so different, please don't try to use '/'.