认识python中的set集合及其用法

python中，集合(set)是一个无序排列，可哈希，
支持集合关系测试,不支持索引和切片操作，没有特定语法格式，
只能通过工厂函数创建.集合里不会出现两个相同的元素，
所以集合常用来对字符串或元组或列表中的元素进行去重操作。

生成一个集合可以使用如下语法：

生成集合语法1：
>>> l1=[1,2,3,4,5,6]
>>> s1=set(l1)
>>> print(s1)
{1, 2, 3, 4, 5, 6}
在这里，使用工厂函数set创建集合，set的参数可以是一个列表，也可以是一个元组或字符串。
生成集合语法2：
>>> s2={6,7,8,9,10}
>>> print(s2)
{8, 9, 10, 6, 7}
生成集合语法3：
>>> s3={i for i in range(10)}
>>> print(s3)
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}

集合类型的方法和操作：

add

为集合增加一个元素，如果集合中本来已经存在这个元素对集合无影响
Add an element to a set.
This has no effect if the element is already present.

>>> s1={1,2,3,4,5,6,7}
>>> s1.add(8)
>>> print(s1)
{1, 2, 3, 4, 5, 6, 7, 8}
>>> s1.add(9)
>>> print(s1)
{1, 2, 3, 4, 5, 6, 7, 8, 9}

clear

清空集合里所有的元素
Remove all elements from this set.

>>> s1={1,2,3,4,5,6,7}
>>> s2={5,6,7,8,9}
>>> s1.clear()
>>> print(s1)
set()
>>> s2.clear()
>>> print(s2)
set()

copy

对集合进行浅拷贝(只复制元素，不复制内存地址)
Return a shallow copy of a set.

>>> s1={1,2,3,4,5,6,7}
>>> print(s1,id(s1))
{1, 2, 3, 4, 5, 6, 7} 140509859430472
>>> s2=s1.copy()
>>> print(s2,id(s2))
{1, 2, 3, 4, 5, 6, 7} 140509842716712

difference

求两个或多个集合的差集，并返回一个新集合
Return the difference of two or more sets as a new set.

>>> s1={1,2,3,4,5,6,7}
>>> s2={5,6,7,8,9,10}
>>> s1.difference(s2)
{1, 2, 3, 4}
>>> s2.difference(s1)
{8, 9, 10}

difference_update

把两个集合的交集部分从集合中移除
Remove all elements of another set from this set.

>>> s1={1,2,3,4,5,6,7}
>>> s2={5,6,7,8,9,10}
>>> s1.difference_update(s2)
>>> print(s1)
{1, 2, 3, 4}
>>> s1={1,2,3,4,5,6,7}
>>> s2={5,6,7,8,9,10}
>>> s2.difference_update(s1)
>>> print(s2)
{8, 9, 10}

discard

从集合中移除一个元素，如果被移除的元素不在集合中，不会报错
Remove an element from a set if it is a member.
If the element is not a member, do nothing.

{1, 2, 3, 4, 5, 6, 7}
>>> s1.discard(7)
>>> print(s1)
{1, 2, 3, 4, 5, 6}
>>> s1.discard(4)
>>> print(s1)
{1, 2, 3, 5, 6}
>>> print(s1)
{1, 2, 3, 5, 6}

intersection

求两个或多个集合中的交集
Return the intersection of two sets as a new set.

>>> s1={1,2,3,4,5,6,7}
>>> s2={5,6,7,8,9,10}
>>> s1.intersection(s2)
{5, 6, 7}
>>> s2.intersection(s1)
{5, 6, 7}

intersection_update

把两个集合的交集做为新的集合
Update a set with the intersection of itself and another.

>>> s1={1,2,3,4,5,6,7}
>>> s2={5,6,7,8,9,10}
>>> s1.intersection_update(s2)
>>> print(s1)
{5, 6, 7}
>>> print(s2)
{5, 6, 7, 8, 9, 10}

>>> s1={1,2,3,4,5,6,7}
>>> s2={5,6,7,8,9,10}
>>> s2.intersection_update(s1)
>>> print(s2)
{5, 6, 7}
>>> print(s1)
{1, 2, 3, 4, 5, 6, 7}

isdisjoint

两个集合没有交集则返回True
Return True if two sets have a null intersection.

>>> s1={1,2,3,4,5,6,7}
>>> s2={5,6,7,8,9,10}
>>> s1.isdisjoint(s2)
False
>>> s1={1,2,3,4}
>>> s2={6,7,8,9}
>>> s1.isdisjoint(s2)
True

issubset

如果本集合是参数集合的子集，返回True
Report whether another set contains this set.

>>> s1={1,2,3,4}
>>> s2={1,2,3,4,5,6,7}
>>> s1.issubset(s2)
True
>>> s2.issubset(s1)
False

issuperset

如果本集合是参数集合的超集，返回True
Report whether this set contains another set.

>>> s1={1,2,3,4}
>>> s2={1,2,3,4,5,6,7}
>>> s1.issuperset(s2)
False
>>> s2.issuperset(s1)
True

pop

从集合中移除一个元素，如果集合为空，则报错
Remove and return an arbitrary set element.
Raises KeyError if the set is empty.

>>> s1={2,3,4,5}
>>> s1.pop()
2
>>> print(s1)
{3, 4, 5}
>>> s1.pop()
3
>>> s1.pop()
4
>>> s1.pop()
5
>>> s1.pop()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'pop from an empty set'

remove

移除集合中的一个元素，如果集合是空的，则报错
Remove an element from a set; it must be a member.  
If the element is not a member, raise a KeyError.

>>> s1={1,2,3,4,5,6}
>>> s1.remove(4)
>>> print(s1)
{1, 2, 3, 5, 6}
>>> s1.remove(9)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 9

symmetric_difference

返回两个集合的对称差集的集合
Return the symmetric difference of two sets as a new set.

>>> s1={1,2,3,4}
>>> s2={6,7,8,9}
>>> s1.symmetric_difference(s2)
{1, 2, 3, 4, 6, 7, 8, 9}
>>> s3={1,2,3,4,5,6}
>>> s4={5,6,7,8,9,10}
>>> s3.symmetric_difference(s4)
{1, 2, 3, 4, 7, 8, 9, 10}

symmetric_difference_update

与参数集合做对称差集，并返回给自身
Update a set with the symmetric difference of itself and another.

>>> s1={1,2,3,4}
>>> s2={6,7,8,9}
>>> s2.symmetric_difference_update(s1)
>>> print(s2)
{1, 2, 3, 4, 6, 7, 8, 9}

>>> s3={1,2,3,4,5,6}
>>> s4={5,6,7,8,9,10}
>>> s3.symmetric_difference_update(s4)
>>> print(s3)
{1, 2, 3, 4, 7, 8, 9, 10}

union

求两个或多个集合的并集
Return the union of sets as a new set.

>>> s1={1,2,3,4,5,6}
>>> s2={5,6,7,8,9}
>>> s1.union(s2)
{1, 2, 3, 4, 5, 6, 7, 8, 9}

>>> s3={1,2,3,4}
>>> s4={6,7,8,9}
>>> s3.union(s4)
{1, 2, 3, 4, 6, 7, 8, 9}

update

与另一个集合求并集，并返回给自身
Update a set with the union of itself and others.

>>> s3={1,2,3,4}
>>> s4={6,7,8,9}
>>> s3.update(s4)
>>> print(s3)
{1, 2, 3, 4, 6, 7, 8, 9}