Are Python sets mutable?

Question

Are sets in Python mutable?

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In other words, if I do this:

x = set([1, 2, 3])
y = x

y |= set([4, 5, 6])

Are x and

Answer 1

Yes, Python sets are mutable because we can add, delete elements into set, but sets can't contain mutable items into itself. Like the below code will give an error:

s = set([[1,2,3],[4,5,6]])

So sets are mutable but can't contain mutable items, because set internally uses hashtable to store its elements so for that set elements need to be hashable. But mutable elements like list are not hashable.

Note:
Mutable elements are not hashable
Immutable elements are hashable

Just like key of a dictionary can't be a list.