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 y still pointing to the same object, or was a new set created and assigned to y?

Answer 1

>>>> x = set([1, 2, 3]) >>>> y = x >>>>  >>>> y |= set([4, 5, 6])  >>>> print x set([1, 2, 3, 4, 5, 6]) >>>> print y set([1, 2, 3, 4, 5, 6]) 

• Sets are unordered.
• Set elements are unique. Duplicate elements are not allowed.
• A set itself may be modified, but the elements contained in the set must be of an immutable type.

set1 = {1,2,3}  set2 = {1,2,[1,2]}  --> unhashable type: 'list' # Set elements should be immutable. 

Conclusion: sets are mutable.