python之集合set

1.测试

 # python2和python3方法列表相同
 ops23 = ['add', 'clear', 'copy', 'difference', 'difference_update', 'discard', 'intersection', 'intersection_update',
     'isdisjoint', 'issubset', 'issuperset', 'pop', 'remove', 'symmetric_difference',
     'symmetric_difference_update', 'union', 'update']

 for op in ops23:
     try:
         print('#'*10)
         S_abc = set('abc')
         S_cde = set('cde')
         print(op,eval('S_abc.{}(S_cde)'.format(op)))
         print('S_abc:',S_abc)
         print('S_cde:',S_cde)
     except Exception as why:
         print(op,why)

2. 总结

(1)元素操作

S.add 添加hashable type，注意set为unhashable type

S.pop随机删除并返回，remove删除指定元素可能报错，discard删除指定元素不会报错

S.clear 清空

S.copy 浅复制shallow copy

(2)判断关系

S.isdisjoint不相交 S.issubset子集 S.issuperset超集

(3)集合操作

命名方法	运算符语法	图例结果	对应update
S.difference(S1)	S-S1	A	S -=S1
S.intersection(S1)	S&S1	B	S &=S1
S.symmetric_difference(S1)	S^S1	A+C	S ^=S1
S.union(S1)	S|S1	A+B+C	S |=S1

(a) S.xxx返回结果集合，S.xxx_update原地更新S，返回None，union对应方法为update而不是union_update

(b)命名方法相比运算符语法，S1可以是由可哈希的项目组成的任意迭代

>>> set('abc').union('cde')
set(['a', 'c', 'b', 'e', 'd'])
>>> set('abc').union(set('cde'))
set(['a', 'c', 'b', 'e', 'd'])
>>>

3.输出分析

 ##########
 ('add', TypeError("unhashable type: 'set'",))
 ##########
 ('clear', TypeError('clear() takes no arguments (1 given)',))
 ##########
 ('copy', TypeError('copy() takes no arguments (1 given)',))
Return a shallow copy of a set.
In [45]: S_abc.copy() == S_abc
Out[45]: True

In [46]: S_abc.copy() is S_abc
Out[46]: False

 ##########
 ('difference', set(['a', 'b']))
 ('S_abc:', set(['a', 'c', 'b']))
 ('S_cde:', set(['c', 'e', 'd']))
 ##########
 ('difference_update', None)
 ('S_abc:', set(['a', 'b']))  #更新S1，留不同
 ('S_cde:', set(['c', 'e', 'd']))

 ##########
 ('discard', None)
 ('S_abc:', set(['a', 'c', 'b']))
 ('S_cde:', set(['c', 'e', 'd']))

 ##########
 ('intersection', set(['c']))
 ('S_abc:', set(['a', 'c', 'b']))
 ('S_cde:', set(['c', 'e', 'd']))
 ##########
 ('intersection_update', None)
 ('S_abc:', set(['c']))  #更新S1，留交集
 ('S_cde:', set(['c', 'e', 'd']))


 ##########
 ('isdisjoint', False)
 ('S_abc:', set(['a', 'c', 'b']))
 ('S_cde:', set(['c', 'e', 'd']))
Return True if two sets have a null intersection.
 ##########
 ('issubset', False)
 ('S_abc:', set(['a', 'c', 'b']))
 ('S_cde:', set(['c', 'e', 'd']))
 ##########
 ('issuperset', False)
 ('S_abc:', set(['a', 'c', 'b']))
 ('S_cde:', set(['c', 'e', 'd']))


 ##########
 ('pop', TypeError('pop() takes no arguments (1 given)',))
Remove and return an arbitrary set element.随机返回
 ##########
 ('remove', KeyError(set(['c', 'e', 'd']),))
 ##########


 ('symmetric_difference', set(['a', 'b', 'e', 'd']))
 ('S_abc:', set(['a', 'c', 'b']))
 ('S_cde:', set(['c', 'e', 'd']))
 ##########
 ('symmetric_difference_update', None)
 ('S_abc:', set(['a', 'b', 'e', 'd']))  #更新S1，所有异或 01 10
 ('S_cde:', set(['c', 'e', 'd']))

 ##########
 ('union', set(['a', 'c', 'b', 'e', 'd']))  #并集
 ('S_abc:', set(['a', 'c', 'b']))
 ('S_cde:', set(['c', 'e', 'd']))
 ##########
 ('update', None)  #更新S1为全集
 ('S_abc:', set(['a', 'c', 'b', 'e', 'd']))
 ('S_cde:', set(['c', 'e', 'd']))