python set()集合

定义一个集合（初始化集合需要用set()）

>>> basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}>>> print(basket)                      # show that duplicates have been removed{'orange', 'banana', 'pear', 'apple'}>>> 'orange' in basket                 # fast membership testingTrue>>> 'crabgrass' in basketFalse

集合操作

>>> # Demonstrate set operations on unique letters from two words...>>> a = set('abracadabra')>>> b = set('alacazam')>>> a                                  # unique letters in a{'a', 'r', 'b', 'c', 'd'}>>> a - b                              # letters in a but not in b{'r', 'd', 'b'}>>> a | b                              # letters in either a or b{'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'}>>> a & b                              # letters in both a and b{'a', 'c'}>>> a ^ b                              # letters in a or b but not both{'r', 'd', 'b', 'm', 'z', 'l'}
类似 列表推导式，这里有一种集合推导式语法:

>>> a = {x for x in 'abracadabra' if x not in 'abc'}>>> a{'r', 'd'}