python3.x 基础三：set集合

集合，set()，记住：

1个特点：去重，把列表变成集合，达到自动去重操作，无序

5个关系：测试两个列表的交差并子反向差集

方法：

| add(...) 常用，已存在元素去重不生效
| Add an element to a set.

| This has no effect if the element is already present. python3.x 基础三：set集合

>>> list1=[3,2,1,1,2,3,4,5]
>>> set(list1)
{1, 2, 3, 4, 5}
>>> list2=[3,4,5,6,7,8]
>>> set(list1).add(2)
>>> set(list1).add(6)
>>> print(set(list1).add(2))
None
>>> print(set(list1).add(6))
None
>>> set1=set(list1)
>>> set2=set(list2)
>>> set1,set2
({1, 2, 3, 4, 5}, {3, 4, 5, 6, 7, 8})
>>> set1.add(3)
>>> print(set1.add(3)
... )
None
>>> print(set1.add(7))
None
>>> set1.add('aaa')
>>> set1
{1, 2, 3, 4, 5, 7, 'aaa'}
>>> id(set1)
140138768484616
>>> set1.add('aaaa')
>>> id(set1)
140138768484616
>>> set1
{1, 2, 3, 4, 5, 7, 'aaa', 'aaaa'}
>>> set1.add('7')
>>> set1
{1, 2, 3, 4, 5, 7, 'aaa', 'aaaa', '7'}
>>> set1.add(7)
>>> set1
{1, 2, 3, 4, 5, 7, 'aaa', 'aaaa', '7'}

View Code

如果是字符串，则拆分成单个字符集合
```
>>> set('abc')
{'a', 'c', 'b'}
```

| clear(...) 清空一个集合
| Remove all elements from this set.
```
>>> set1.clear()
>>> set1
set()
```
| copy(...) 影子复制，指向同一个内存地址

| Return a shallow copy of a set. |

>>> list1
[3, 2, 1, 1, 2, 3, 4, 5]
>>> list2
[3, 4, 5, 6, 7, 8]
>>> set1=set(list1)>>> id(set1)
140138768485512>>> set3=set1.copy()
>>> id(set3)
140138695576712

| difference(...) 差集，格式set1.difference(set2)，求in list1 not in list2的集合
| Return the difference of two or more sets as a new set. |

| (i.e. all elements that are in this set but not the others.)

>>> set1
{1, 2, 3, 4, 5}
>>> set2
{3, 4, 5, 6, 7, 8}
>>> set1.difference(set2)
{1, 2}

| difference_update(...) 删除在本集合同时也在其他集合的元素，差集

| Remove all elements of another set from this set. |

>>> set1=set(list1)
>>> set2=set(list2)
>>> set1,set2
({1, 2, 3, 4, 5}, {3, 4, 5, 6, 7, 8})
>>> set1=set(list1)>>> set2=set(list2)
>>> set2.difference_update(set1)
>>> set2
{6, 7, 8}

| discard(...) 删除一个在本集合中的元素
| Remove an element from a set if it is a member.
|

| If the element is not a member, do nothing. |

>>> set3=set([1,2,3,'a','b','c'])
>>> set3.discard(1)
>>> set3
{2, 3, 'c', 'b', 'a'}
>>> set3.discard('a')
>>> set3
{2, 3, 'c', 'b'}
>>> set3.discard('dd')
>>> set3
{2, 3, 'c', 'b'}

| intersection(...)并集，同时在两个集合中的元素
| Return the intersection of two sets as a new set.
|

| (i.e. all elements that are in both sets.) |

>>> set1
{1, 2, 3, 4, 5}
>>> set2
{3, 4, 5, 6, 7, 8}
>>> set1.intersection(set2)
{3, 4, 5}
>>> set2.intersection(set1)
{3, 4, 5}

| intersection_update(...) 交集

| Update a set with the intersection of itself and another. |

>>> set1,set2
({1, 2, 3, 4, 5}, {3, 4, 5, 6, 7, 8})
>>> set1.intersection_update(set2)
>>> set1
{3, 4, 5}

| isdisjoint(...) 返回布尔值，判断两个集合是否没有并集
| Return True if two sets have a null intersection.

>>> set1,set2,set3,set4
({3, 4, 5}, {3, 4, 5, 6, 7, 8}, {2, 3, 'c', 'b'}, {'y', 'x', 'z'})
>>> set1.isdisjoint(set2)
False
>>> set1.isdisjoint(set4)
True

| issubset(...) 返回布尔值，判断前一个集合是否是后一个集合的子集

| Report whether another set contains this set. |

>>> set1
{3, 4, 5}
>>> set5
{3, 4}
>>> set5.issubset(set1)
True

| issuperset(...) 返回布尔值，判断前一个集合是否是后一个集合的父集

| Report whether this set contains another set. |

>>> set1
{3, 4, 5}
>>> set5
{3, 4}
>>> set1.issuperset(set5)
True

| pop(...) 随机删除一个集合元素，返回被删除元素，空集合删除则报错
| Remove and return an arbitrary set element.

| Raises KeyError if the set is empty. |

>>> set1
{3, 4, 5}
>>> set1.pop()
3
>>> set1
{4, 5}
>>> set1.pop()
4
>>> set1.pop()
5
>>> set1.pop()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'pop from an empty set'

| remove(...) 删除指定在集合中的元素

| Remove an element from a set; it must be a member. |

>>> set1=set(list1)
>>> set1
{1, 2, 3, 4, 5}
>>> set1.remove(1)
>>> set1
{2, 3, 4, 5}
>>> set1.remove('a')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'a'

| symmetric_difference(...) 对称差集，集合A与集合B不相交的部分，交集的反集
| Return the symmetric difference of two sets as a new set.

| (i.e. all elements that are in exactly one of the sets.)

>>> set1
{1, 2, 3, 4, 5}
>>> set6={4,5,6,7,8}
>>> set1.symmetric_difference(set6)
{1, 2, 3, 6, 7, 8}
>>> set6.symmetric_difference(set1)
{1, 2, 3, 6, 7, 8}
>>> set1,set7
({1, 2, 3, 4, 5}, {'a', 'c', 'b'})
>>> set1.symmetric_difference(set7)
{'c', 2, 3, 1, 4, 5, 'b', 'a'}

| symmetric_difference_update(...)
| Update a set with the symmetric difference of itself and another.
|

| union(...) 并集
| Return the union of sets as a new set.

| (i.e. all elements that are in either set.)

>>> set1
{1, 2, 3, 4, 5}
>>> set2
{3, 4, 5, 6, 7, 8}
>>> set1.union(set2)
{1, 2, 3, 4, 5, 6, 7, 8}

| update(...) 用交集更新到set1的集合

| Update a set with the union of itself and others. |

>>> set1
{1, 2, 3, 4, 5}
>>> set2
{3, 4, 5, 6, 7, 8}
>>> set1.update(set2)
>>> set1
{1, 2, 3, 4, 5, 6, 7, 8}
>>>

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python3.x 基础三：set集合

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