Sets

 
#!/usr/bin/env python
basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
#
# create a set without duplicates
#
fruit = set(basket)
#
# membership testing
#
print( 'pear' in fruit)  # -> True

a = set('abracadabra')
b = set('alacazam')
print( a)                # -> set(['a', 'r', 'b', 'c', 'd']), unique letters in a
print( a - b)            # -> set(['r', 'b', 'd']), letters in a but not in b
print( a | b)            # -> set(['a', 'c', 'b', 'd', 'm', 'l', 'r', 'z'])
                         #    letters in either a or b
print( a & b)            # -> set(['a', 'c'] letters in both a and b
print( a ^ b)            # -> set(['b', 'd', 'm', 'l', 'r', 'z']) 
                         #    letters in a or b but not both