Python基础day03:集合
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一、概述
集合是无序的,天生不重复的数据组合,它的作用如下:
- 去重,即:把一个列表变成集合,就去重了
- 关系测试,即:测试两组集合的交集、并集和差集等
二、定义
1、语法
>>> name_1 = [1,2,3,4,7,8,7,10] #把列表转换为集合 >>> name_1 = set(name_1) #转换后,去重 >>> print(name_1,type(name_1)) {1, 2, 3, 4, 7, 8, 10} <class ‘set‘>
三、关系测试
1、交集(intersection())
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_2 = [1,3,5,8,10] >>> name_1 = set(name_1) >>> name_2 = set(name_2) #输出结果 >>> name_1.intersection(name_2) {8, 1, 10, 3}
2、并集(union())
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_2 = [1,3,5,8,10] >>> name_1 = set(name_1) >>> name_2 = set(name_2) #输出结果 >>> name_1.union(name_2) {1, 2, 3, 4, 5, 7, 8, 10}
3、差集(difference())
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_2 = [1,3,5,8,10] >>> name_1 = set(name_1) >>> name_2 = set(name_2) #输出结果 >>> name_1.difference(name_2) {2, 4, 7}
注:差集取的是数值在第一个集合中,但是不在第二个集合中(在我不在你)
4、issubset()
判断一个集合是否是另一个集合的子集
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_3 = [1,2,3,4] >>> name_1 = set(name_1) >>> name_3 = set(name_3) #输出结果 >>> name_3.issubset(name_1) True
5、issuperset()
判断一个集合是否是另一个集合的父集
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_3 = [1,2,3,4] >>> name_1 = set(name_1) >>> name_3 = set(name_3) #输出结果 >>> name_1.issuperset(name_3) True
6、对称差集(symmetric_difference())
把两个集合没有交集的数值取出来
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_2 = [1,3,5,8,10] >>> name_1 = set(name_1) >>> name_2 = set(name_2) #输出结果 >>> name_1.symmetric_difference(name_2) {2, 4, 5, 7}
7、isdisjoint()
判断两个集合是否有交集,没有交集,则返回True
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_2 = [1,3,5,8,10] >>> name_3 = [11] >>> name_1 = set(name_1) >>> name_2 = set(name_2) >>> name_3 = set(name_3) #有交集 >>> name_1.isdisjoint(name_2) False #无交集 >>> name_1.isdisjoint(name_3) True
四、关系测试(特殊符号)
1、交集(&)
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_2 = [1,3,5,8,10] >>> name_1 = set(name_1) >>> name_2 = set(name_2) #结果输出 >>> name_1 & name_2 {8, 1, 10, 3}
2、并集(|)
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_2 = [1,3,5,8,10] >>> name_1 = set(name_1) >>> name_2 = set(name_2) #结果输出 >>> name_1 | name_2 {1, 2, 3, 4, 5, 7, 8, 10}
3、差集(-)
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_2 = [1,3,5,8,10] >>> name_1 = set(name_1) >>> name_2 = set(name_2) #结果输出 >>> name_1 - name_2 {2, 4, 7}
4、对称差集(^)
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_2 = [1,3,5,8,10] >>> name_1 = set(name_1) >>> name_2 = set(name_2) #输出 >>> name_1 ^ name_2 {2, 4, 5, 7}
5、是否是子集(<=)
>>> name_1 = [1,2,3,4,7,8,10] >>> name_3 = [1,2,3,4] >>> name_1 = set(name_1) >>> name_3 = set(name_3) #输出 >>> name_3 <= name_1 True
6、是否是父集(>=)
>>> name_1 = [1,2,3,4,7,8,10] >>> name_3 = [1,2,3,4] >>> name_1 = set(name_1) >>> name_3 = set(name_3) #输出 >>> name_1 >= name_3 True
五、基本操作
1、添加(add())
>>> name_2 = [1,3,5,8,10] >>> name_2 = set(name_2) #添加已存在,不报错 >>> name_2.add(1) >>> name_2 {8, 1, 10, 3, 5} #添加不存在,添加一个新的数值 >>> name_2.add(11) >>> name_2 {1, 3, 5, 8, 10, 11}
2、添加多项(update())
>>> name_2 = [1,3,5,8,10] >>> name_2 = set(name_2) >>> name_2.update([12,13,14]) #输出结果 >>> name_2 {1, 3, 5, 8, 10, 12, 13, 14}
3、删除(remove(),pop(),discard())
①remove()
>>> name_2 = [1,3,5,8,10] >>> name_2 = set(name_2) >>> name_2 {8, 1, 10, 3, 5} >>> name_2.remove(1) #输出 >>> name_2 {8, 10, 3, 5} #删除不存在的元素,会报错 >>> name_2.remove(1) Traceback (most recent call last): File "<input>", line 1, in <module> KeyError: 1
注:用remove删除时,当元素不存在,会报错
②pop()
>>> name_2 = [1,3,5,8,10] >>> name_2 = set(name_2) >>> name_2 {8, 1, 10, 3, 5} #输出 >>> name_2.pop() 8
注:pop是随机删除集合中的某个元素,并且打印
③discard()
>>> name_2 = [1,3,5,8,10] >>> name_2 = set(name_2) >>> name_2.discard(10) #输出结果 >>> name_2 {8, 1, 3, 5} #删除不存在元素,不报错 >>> name_2.discard(10)
注:用discard删除不存在的元素,不会出现报错
4、长度(len())
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_1 = set(name_1) #结果输出 >>> len(name_1) 7
5、x in s
测试 x 是否是 s 的成员
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_1 = set(name_1) #结果输出 >>> 1 in name_1 True
6、x not in s
测试 x 是否不是 s 的成员
>>> name_1 = [1,2,3,4,7,8,7,10] >>> name_1 = set(name_1) #输出 >>> 12 not in name_1 True
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