I could probably live with that.  However, there are other kinds of objects being used as keys in the same dictionary, and I can't just repr() them all, because it is not true that a == b implies repr(a) == repr(b).  (E.g., a = 3, b = 3.0.)

Practicalities aside, it just seems silly to me that a simple type like slice should have all the prerequisites for being hashable and yet isn't, especially when much more complex types like methods are both comparable and hashable.