Python sets

1. Sometimes we want to deal with sets of things. We can make a set from a list. Note how Python writes a set with braces { }.

   >>> beatles = 'john paul george ringo'.split()
   >>> beatles
   ['john', 'paul', 'george', 'ringo']
   >>> set(beatles)
   {'ringo', 'paul', 'john', 'george'}
   >>> ledzeps = 'jimmy robert john john'.split()
   >>> ledzeps
   ['jimmy', 'robert', 'john', 'john']
   >>> set(ledzeps)
   {'john', 'robert', 'jimmy'}
   

   Note how the order in which the elements are presented may not be the order of input. A set has no inherent order. Python chooses its own order.

2. We can also make sets from strings. We get a set of characters.

   >>> aa = set('anybody')
   >>> bb = set('banana')
   >>> aa
   {'a', 'b', 'd', 'n', 'o', 'y'}
   >>> bb
   {'a', 'b', 'n'}
   

3. And we can carry out standard set operations such as difference, intersection, union and symmetric difference:

   >>> aa - bb
   {'y', 'd', 'o'}
   >>> aa & bb
   {'a', 'b', 'n'}
   >>> aa | bb
   {'a', 'b', 'd', 'y', 'o', 'n'}
   >>> aa ^ bb
   {'y', 'd', 'o'}