Python Set Types

A set object is an unordered collection of distinct hashtable objects. Common uses include membership testing, removing duplicates from a sequence, and computing mathematical operations such as intersection, union, difference, and symmetric difference.

Like other collections, sets support x in set, len(set), and for x in set. Being an unordered collection, sets do not record element position or order of insertion. Accordingly, sets do not support indexing, slicing, or other sequence-like behavior.

operations:

len(x)                    #长度
'i' in x
s.issubset(x)             #s是否为x的子集
x.union(y)                #交
x.difference(y)           #差
x.symmetric_difference(y) #对称差
s.update(x)               #更新s，加上x中的元素
s.add()                  #增加元素
s.remove()               #删除已有元素，如果没有会返回异常
s.discard(2)               #如果存在元素，就删除；没有不报异常
s.clear()                  #清除set
x.pop()                    #随机删除一元素