[boothby]

Problem being that sets aren't consistently ordered and conversion to a tuple can result in an exponential (specifically, factorial) explosion in the number of possible keys associated with a single set. Nor can you sort all objects. Safe conversion of sets to tuples for use as keys is possible but the only technique I know requires an auxiliary store of objects (mapping objects to the order in which they were first observed), which doesn't parallelize well.

[morshu9001]

tuple(sorted(s)) and if you can't even sort the values, they're probably not hashable. I get that this involves a copy, but so does frozenset, and you can cross that bridge in various ways if it's ever a problem.

[boothby]

Here are some types that support hashing:

  str
  bytes
  int, float
  complex
  tuple
  frozenset

Aside from int and float, you cannot perform comparisons between objects of different types. Moreover, you cannot sort complex numbers at all.

I have crossed that bridge, and I'm telling you (again) that a sorted tuple is not a generic solution.

[morshu9001]

I'm not saying the problem with tuple doesn't exist, but that there doesn't need to be a built-in way to deal with it. If for some unfortunate reason you've got a mixed-type set that you also want to use as a dict key, you can write a helper.