set 集合
Set
一、简介
- set中的元素：可hash(int, str, tuple, bool)，不重复，底层存储无序
- set集合中的元素必须是可hash，但set本身是不可hash，是可变的数据类型
二、应用(重点)
利用set中元素不可重复，可给list去重
lst = [11, 11, 22, 22, 33, 33, 44, 44, 55, 55] lst = list(set(lst)) print(lst) # [33, 11, 44, 22, 55] 结果无序，但已去重
三、增删改查
1）增
- add
重复的内容不会被添加到set集合中，新增对象须为可hash数据类型
s = {11, 22, 33, 44}
s.add("hello")
print(add) # {33, 11, 44, 'hello', 22}
s.add(11)
print(s) # {33, 11, 44, 'hello', 22}
- update
迭代更新，新增对象可为可hash或不可hash数据类型
s = {11, 22, 33, 44}
s.update("hello")
print(s) # {33, 'l', 11, 44, 'e', 22, 'o', 'h'}
s = {11, 22, 33, 44}
s.update([55, 66, 77])
print(s) # {33, 66, 11, 44, 77, 22, 55}
2）删
- pop
随机弹出一个
s = {11, 22, 33, 44}
num = s.pop()
print(s) # {11, 44, 22}
print(num) # 33
- remove
根据元素内容进行删除，若元素不存在，则报错
s = {11, 22, 33, 44}
s.remove(11)
print(s) # {33, 44, 22}
- clear
清空set集合，如果set集合是空的，打印出来是set()，须与dict区分
s = {11, 22, 33, 44}
s.clear()
print(s) # set()
3) 改
- set集合中数据没有索引，也没法定位一个元素，所以没有办法进行直接修改
- 可采用先删除后添加方式完成修改
s = {11, 22, 33, 44}
s.remove(11)
s.add(55)
print(s) # {33, 44, 22, 55}
4）查
set是一个可迭代对象，可进行for循环
for el in s: print(el)
四、常用操作
1）交集
- &
s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}
print(s1 & s2) # {33, 44}
- intersection
s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}
print(s1.intersection(s2)) # {33, 44}
2)并集
- |
s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}
print(s1 | s2) # {33, 22, 55, 11, 44}
- union
s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}
print(s1.union(s2)) # {33, 22, 55, 11, 44}
3)差集
s1 - s2：得到s1中单独存在的
- -
s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}
print(s1 - s2) # {11, 22}
- difference
s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}
print(s1.difference(s2)) # {11, 22}
4)反交集
s1 ^ s2：得到一个新的集合，里面元素为两集合（s1, s2）不相同的元素
- ^
s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}
print(s1 ^ s2) # {22, 55, 11}
- symmetric_difference
s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}
print(s1.symmetric_difference(s2)) # {22, 55, 11}
5)子集
s1 < s2:判断s1是否为s2子集，返回True or False
- <
s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}
print(s1 < s2) # False
- issubset
s1 = {11, 22, 33, 44}
s2 = {11, 22, 33, 44, 55}
print(s1.issubset(s2)) # True
6)超集
s1 > s2：判断s1是否为s2的超集，也即s2是否为s1的子集，返回True or False
- >
s1 = {11, 22, 33, 44}
s2 = {11, 22, 33}
print(s1 > s2) # True
- issuperset
s1 = {11, 22, 33, 44}
s2 = {11, 22, 33}
print(s1.issuperset(s2)) # True
7) frozenset
- frozenset是一种不可变，可hash的集合
- 通过frozenset可将可变的数据类型转换成不可变，可hash的frozenset集合
s = [44, 55, 66] s1 = {11, 22, 33, s} # 报错 TypeError: unhashable type: 'list'
s = frozenset([44, 55, 66])
print(s) # frozenset({66, 44, 55}) s1 = {11, 22, 33, s} # 正常
s = frozenset([1,2,3,4,5]) print(s) # frozenset({1, 2, 3, 4, 5}) for el in s: print(el) # 1 2 3 4 5
