PYTHON-set()-集合学习

　　集合就类似于数学中的集合，具有互异性和无序性。

1.创建集合：

#创建一个空的集合必须用set()，因为{}为dict。且set()只接受一个参数

>>> a = {}
>>> type(a)
<class 'dict'>
>>> a = set()
>>> type(a)
<class 'set'>
>>> 

#集合中放的只能是数字、元组、字符串，不能放字典，列表

>>> set1 = {1, 2, 3, (4, 5, 6), "good news",[1,2,3]}
Traceback (most recent call last):
  File "<pyshell#83>", line 1, in <module>
    set1 = {1, 2, 3, (4, 5, 6), "good news",[1,2,3]}
TypeError: unhashable type: 'list'

>>> set1 = {1, 2, 3, (4, 5, 6), "good news"}
>>> set1
{'good news', 1, 2, 3, (4, 5, 6)}

>>> set1 = {1, 2, 3, (4, 5, 6), "good news",{1:"123",2:"456"}}
Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    set1 = {1, 2, 3, (4, 5, 6), "good news",{1:"123",2:"456"}}
TypeError: unhashable type: 'dict'

#但是单个的字典、集合、列表还是可以的

>>> a = set([1,2,3])
>>> a
{1, 2, 3}
>>> a = set({1,2,3})
>>> a
{1, 2, 3}
>>> a = set({1:"123",2:"456"})
>>> a
{1, 2}

#组合起来就不行了

>>> a = set({[1,2,3]})
Traceback (most recent call last):
  File "<pyshell#9>", line 1, in <module>
    a = set({[1,2,3]})
TypeError: unhashable type: 'list'
>>> a = set({[1,2,3],(1,)})
Traceback (most recent call last):
  File "<pyshell#10>", line 1, in <module>
    a = set({[1,2,3],(1,)})
TypeError: unhashable type: 'list'
>>> 

2.作用

2.1 列表过滤：

#可以将列表中的重复元素过滤掉，很简单的

>>> a = [1,1,1,2,3,6,5,8,6,2]
>>> set(a)
{1, 2, 3, 5, 6, 8}
>>> list(set(a))
[1, 2, 3, 5, 6, 8]

2.2 add(值)

>>> c = {1,3}
>>> c.add(2)
>>> c
{1, 2, 3} #增肌爱元素的无序性，就是没加在最后
>>> c.add(2)
>>> c
{1, 2, 3} #互异性

2.3 remove(值)

>>> c
{1, 2, 3}
>>> c.remove(2)
>>> c
{1, 3}
>>> c.remove(5)
Traceback (most recent call last):
  File "<pyshell#23>", line 1, in <module>
    c.remove(5)
KeyError: 5
>>> 

2.4 集合运算：

>>> a = {1,2,34,58}
>>> b = {1,3,7,6}
>>> a & b #交集
{1}
>>> a | b #并集
{1, 2, 34, 3, 6, 7, 58}
>>> a - b　#a中a&b的补集
{2, 34, 58}
>>> b -a  #b中a&b的补集
{3, 6, 7}
>>> 

参考网址：

https://www.cnblogs.com/my_captain/p/9296282.html

https://www.cnblogs.com/TTyb/p/6283539.html