set集合

集合set用{}表示，无序是集合最大特点

集合特点1:无序

>>> {1,2,3,4,5}
{1, 2, 3, 4, 5}
>>> type({1,2,3,4,5})
<class 'set'>

集合不支持索引和切片取值

>>> {1,2,3,4,5}[0]
<stdin>:1: SyntaxWarning: 'set' object is not subscriptable; perhaps you missed a comma?
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'set' object is not subscriptable
>>> {1,2,3,4,5}[0:2]
<stdin>:1: SyntaxWarning: 'set' object is not subscriptable; perhaps you missed a comma?
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'set' object is not subscriptable

集合第二个特点： 不重复

>>> {1,2,3,1,2}
{1, 2, 3}

集合操作

>>> len({1,2,3,2})
3
>>> 1 in {1,2,3}
True
>>> 1 not in {1,2,3}
False
>>> {1,2,3,4,5,6}-{4,5}     # 差集
{1, 2, 3, 6}
>>> {1,2,3,4,5,6} & {4,5}   # 交集
{4, 5}
>>> {1,2,3,4,5,6} | {4,5,7} # 并集（全集）
{1, 2, 3, 4, 5, 6, 7}

如何定一个空集合

>>> type({})
<class 'dict'>

>>> set()
set()
>>> type(set())
<class 'set'>
>>> len(set())
0
>>>