>>> a = {1, 2, 3, 4, 5, 6}
>>> b = {4, 5, 6, 7, 8, 9}
>>>
>>> a.update(b)          # a "union" operation
>>> a
{1, 2, 3, 4, 5, 6, 7, 8, 9}
>>>
>>> a &= b               # the "intersection" operation
>>> a
{4, 5, 6, 7, 8, 9}
>>>
>>> a -= set((7, 8, 9))  # the "difference" operation
>>> a
{4, 5, 6}
>>>
>>> a ^= b               # the "symmetric difference" operation
>>> a
{7, 8, 9}