python-set集合

Python set集合

python的set和其他语言类似, 是一个无序不重复元素集, 基本功能包括关系测试和消除重复元素. 集合对象还支持union(联合), intersection(交), difference(差)和sysmmetric difference(对称差集)等数学运算.

sets 支持 x in set, len(set), 和 for x in set。作为一个无序的集合，sets 不记录元素位置或者插入点。因此，sets 不支持 indexing, slicing, 或其它类序列（sequence-like）的操作。

>>> a = {'111','222',333}
>>> a
{'111', '222', 333}
>>> type(a)
<class 'set'>
>>>
>>> s = ['1','1','2','3','2233']
>>> s
['1', '1', '2', '3', '2233']
>>> b = set(s)
>>> b
{'2233', '2', '1', '3'}
>>> type(b)
<class 'set'>
>>> b.
b.add(                          b.intersection(                 b.remove(
b.clear(                        b.intersection_update(          b.symmetric_difference(
b.copy(                         b.isdisjoint(                   b.symmetric_difference_update(
b.difference(                   b.issubset(                     b.union(
b.difference_update(            b.issuperset(                   b.update(
b.discard(                      b.pop(                          
>>> b.add('666')

add增加一个

>>> a = {'1','2','3'}
>>> type(a)
<class 'set'>
>>> a.add('4')
>>> a
{'1', '3', '4', '2'}
>>> a.add('5','6')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: add() takes exactly one argument (2 given)
>>>
>>> a.add('2')
>>> a
{'3', '2', '4', '1'}
>>>

update增加多个，参数是list

>>> a
{'3', '2', '4', '1'}
>>> a.update('5','6') 
>>> a
{'1', '5', '6', '4', '2', '3'}
>>> a.update('7','8')
>>> a
{'1', '7', '8', '5', '6', '4', '2', '3'}
>>>
>>> b = {'11','22'}                   
>>> a
{'1', '7', '8', '5', '6', '4', '2', '3'}
>>> a.add(b)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'set'
>>> a.update(b) 
>>> a
{'1', '11', '7', '8', '5', '6', '4', '2', '3', '22'}
>>>

remove()用于删除一个set中的元素

这个值在set中必须存在，如果不存在的话，会引发KeyError错误。

>>> a
{'1', '11', '7', '8', '5', '6', '4', '2', '3', '22'}
>>> a.remove('1','2','3')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: remove() takes exactly one argument (3 given)
>>> a.remove('1')        
>>> a
{'11', '7', '8', '5', '6', '4', '2', '3', '22'}
>>> a.remove('33')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: '33'
>>>

discard()用于删除一个set中的元素

这个值不必一定存在，不存在的情况下删除也不会触发错误

>>> a
{'11', '7', '8', '5', '6', '4', '2', '3', '22'}
>>> a.discard('44')
>>> a.discard('2','3')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: discard() takes exactly one argument (2 given)
>>> a.discard('2')    
>>> a
{'11', '7', '8', '5', '6', '4', '3', '22'}
>>>

pop随机删除

从开始。这个函数随机返回一个元素值，然后把这个值删除，如果set为空，调用这个函数会返回Key错误。

>>> a
{'11', '7', '8', '5', '6', '4', '3', '22'}
>>> a.pop()
'11'
>>> a.pop()
'7'
>>> a.pop('5','6')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: pop() takes no arguments (2 given)
>>> a.pop('5')    
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: pop() takes no arguments (1 given)
>>>	
>>> a
set()
>>> a.pop()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'pop from an empty set'
>>>
>>> a
{'22', '4', '5', '11', '6', '8', '7', '3'}
>>> re = a.pop()
>>> re
'22'
>>>  						#移除元素，并且可以把移除的元素赋值给另一个变量

clear清空

>>> a
{'8', '5', '6', '4', '3', '22'}
>>> a.clear()
>>> a
set()
 

intersection 交集

>>> a
{'4', '5', '11', '6', '8', '7', '3'}
>>> b
{'8', '6', '7'}
>>> c = a.intersection(b)
>>> c
{'8', '6', '7'}
>>>

 intersection_update   取出交集并更新

>>> a
{'4', '5', '11', '6', '8', '7', '3'}
>>> b
{'8', '6', '7'}
>>> a.intersection_update(b)
>>> a
{'8', '6', '7'}
>>>

 in/not in

>>> '8' in a
True
>>> '9' not  in a  
True
>>> '8' not  in a 
False
>>>

 difference 不在集合中

>>> a
{'222', '6', '111', '8', '7'}
>>> b
{'777', '6', '8', '666', '7'}
>>> a.difference(b)
{'111', '222'}
>>> b.difference(a)
{'777', '666'}
>>>  

 symmetric_difference 差集

>>> a
{'222', '6', '111', '8', '7'}
>>> b
{'777', '6', '8', '666', '7'}
>>> a.symmetric_difference(b)
{'222', '777', '111', '666'}
>>>  

 issubset和issuperset 集合元素是否在另一个集合中

>>> a
{'222', '6', '111', '8', '7'}
>>> b
{'777', '6', '8', '666', '7'}
>>> c = {'6','7','8'}
>>> c.issubset(a)
True
>>> c.issubset(b)
True
>>> b.issubset(a)
False
>>> c.issuperset(a)
False
>>> c.issuperset(b)
False
>>> a.issuperset(c)
True
>>>

 union合集

>>> a
{'222', '6', '111', '8', '7'}
>>> b
{'777', '6', '8', '666', '7'}
>>> c.clear()
>>> c = a.union(b)
>>> c
{'222', '6', '777', '666', '111', '8', '7'}
>>>