set 常用操作

#-  letters in a but not in b
#|  letters in either a or b
#&  letters in both a and b
#^  letters in a or b but not both

basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
fruit = set(basket)

a = set('abracadabra')
b = set('alacazam')
print a
print a - b
print a | b
print a $ b
print a ^ b