[catnaroek]

> I'm not sure if you are asking about Python, or Ruby.

Ruby, since you said it allows mutable keys in dictionaries.

> Anyway, both languages use value-based hashing for dictionaries.

Neither Python nor Ruby has compound values. Object identities are primitive values.

> but I guess you are just expected to not mutate the keys?

I guess C programmers are expected not to use memory after they free it.