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

Python sets are classified into two types. Mutable and immutable. A set created with 'set' is mutable while the one created with 'frozenset' is immutable.

>>> s = set(list('hello'))
>>> type(s)

The following methods are for mutable sets.

s.add(item) -- Adds item to s. Has no effect if listis already in s.

s.clear() -- Removes all items from s.

s.difference_update(t) -- Removes all the items from s that are also in t.

s.discard(item) -- Removes item from s. If item is not a member of s, nothing happens.

All these operations modify the set s in place. The parameter t can be any object that supports iteration.