How does Python sort a list of sets?

Question

Python sorts lists of tuples by looking at the elements of the tuples, in order. Since sets are unordered, how does Python sort a list of sets?

Edit: The question an

Answer 1

The __le__ operator on sets define the partial ordering "subset". Therefore the sorted order is undefined.

{3} < {5} is false, but so is {5} < {3} so the sort algorithm will usually not rearrange them.

Citation from Python3 documentaton about sets:

The subset and equality comparisons do not generalize to a total ordering function. For example, any two nonempty disjoint sets are not equal and are not subsets of each other, so all of the following return False: ab.

Since sets only define partial ordering (subset relationships), the output of the list.sort() method is undefined for lists of sets.