集合的创建：set()和frozenset()
区别：frozenset()创建不可变的集合，一旦创建其元素不可改变；而set()创建的集合中的元素可以通过一定的方法进行改变。
>>> frozenset('chinese') frozenset({'c', 'h', 's', 'e', 'n', 'i'}) >>> set('chinese') {'c', 'h', 's', 'e', 'n', 'i'} >>> type(set('chinese')) <class 'set'> >>> type(frozenset('chinese')) <class 'frozenset'> >>> len(frozenset('chinese')) 6 >>> len(set('chinese')) 6 >>> frozenset('chinese')==set('chinese') True >>>
>>> a = set('hello') >>> a {'h', 'e', 'l', 'o'} >>> b = set(['hello',123,123,4]) >>> b {'hello', 123, 4} >>> c = frozenset('hello') >>> c frozenset({'h', 'e', 'l', 'o'}) >>> d = frozenset(['hello',123,123,4]) >>> d frozenset({'hello', 123, 4}) >>> e = set(('hello',123,123,4)) >>> e {'hello', 123, 4} >>> f = frozenset(('hello',123,123,4)) >>> f frozenset({'hello', 123, 4}) >>>
访问集合中的值
>>> a = set('hello') >>> a {'h', 'o', 'l', 'e'} >>> 'e' in a True >>> 'g' in a False >>> 'g' not in a True >>> for i in a:print(i) h o l e >>>
更新集合：
追加
>>> a = set('hello') >>> a {'h', 'e', 'l', 'o'} >>> a.add('zyj') >>> a {'h', 'e', 'l', 'o', 'zyj'} >>> a1 = set('zyj') >>> a.add(a1) Traceback (most recent call last): File "<pyshell#15>", line 1, in <module> a.add(a1) TypeError: unhashable type: 'set' >>> a.add(['zyj','!']) Traceback (most recent call last): File "<pyshell#16>", line 1, in <module> a.add(['zyj','!']) TypeError: unhashable type: 'list' >>> a.add(('zyj','!')) >>> a {'zyj', 'h', 'l', 'o', 'e', ('zyj', '!')} >>>
>>> c.add('zyj')
Traceback (most recent call last):
File "<pyshell#21>", line 1, in <module>
c.add('zyj')
AttributeError: 'frozenset' object has no attribute 'add'
>>>
更新：
>>> x = set('hello') >>> x {'h', 'e', 'l', 'o'} >>> x.update('zyj') >>> x {'h', 'l', 'j', 'y', 'o', 'e', 'z'} >>> x.add('zyj') >>> x {'zyj', 'h', 'l', 'j', 'y', 'o', 'e', 'z'} >>>
移除：
>>> x {'zyj', 'h', 'l', 'j', 'y', 'o', 'e', 'z'} >>> x.remove('zyj') >>> x {'h', 'l', 'j', 'y', 'o', 'e', 'z'} >>> x.pop('l') Traceback (most recent call last): File "<pyshell#33>", line 1, in <module> x.pop('l') TypeError: pop() takes no arguments (1 given) >>> x.pop() #删除任意一个对象并返回它 'h'
>>> b
{'j', 'y'}
>>> b.discard('sl')#删除一个元素，元素不存在时不会报错
>>> b
{'j', 'y'}
>>> b.remove('sl')#删除一个元素，元素不存在时会报错
Traceback (most recent call last):
File "<pyshell#55>", line 1, in <module>
b.remove('sl')
KeyError: 'sl'
>>>
删除集合：
>>> del(x) >>> x Traceback (most recent call last): File "<pyshell#36>", line 1, in <module> x NameError: name 'x' is not defined >>> a = set('zyj') >>> a {'z', 'j', 'y'} >>> a.clear()#清除集合中的所有元素，之前的集合变为空集合 >>> a set()
集合类型操作符：
集合等价、不等价（==、!=）
>>> a = set('hello') >>> a {'l', 'e', 'o', 'h'} >>> b =frozenset('helo') >>> b frozenset({'l', 'e', 'o', 'h'}) >>> a == b True >>> a != b False >>>
子集、超集(<、<=、>、>=)：s.issubset(t) s.issuperset(t)
>>> set('he') <= set('hello') True >>> set('helor') <set('hello') False >>> set('helor') >= set('hello') True >>> frozenset(set('hello')) frozenset({'l', 'e', 'o', 'h'}) >>> set('he') == set('eh') True >>>
>>> a =set('hi') >>> a {'i', 'h'} >>> b {'l', 'e', 'o', 'h'} >>> a.issubset(b) False >>> b.issuperset(a) False >>> c = set('h') >>> c {'h'} >>> b {'l', 'e', 'o', 'h'} >>> c.issubset(b) True >>> b.issuperset(c) True >>>
集合类型操作符
联合符号（|）：两个集合联合生成一个新集合，该集合中的每个元素都至少是其中一个集合的成员，联合符号等价的方法为union()
>>> set([1,2,3]) | set('hello') {1, 2, 3, 'l', 'e', 'o', 'h'} >>> set([1,2,3]).union(set('hello')) {1, 2, 3, 'l', 'e', 'o', 'h'}
交集（&）：两个集合联合生成一个新集合，该集合中的每个元素同时是两个集合的成员，交集符号等价的方法为intersection()
>>> set([1,2,3]) & set('hello') set() >>> set('hello') & set('hi') {'h'} >>> set('hello').intersection(set('hi')) {'h'} >>>
差补/相对补集（-）：指两个集合之间的差。等价方法为：difference()
>>> set('hello')-set('h') {'l', 'e', 'o'} >>> set('h')-set('hello') set() >>> set('hello').difference(set('h')) {'l', 'e', 'o'} >>>
对称差分（^）:生成集合中的元素不能同时属于两个集合，等价方法为：symmetric_difference()
>>> set('hello')^set('hi') {'l', 'i', 'e', 'o'} >>> set('hello').symmetric_difference('hi') {'l', 'i', 'e', 'o'} >>>
注意：+不属于集合的操作符。
>>> set('hello')+set('h') Traceback (most recent call last): File "<pyshell#34>", line 1, in <module> set('hello')+set('h') TypeError: unsupported operand type(s) for +: 'set' and 'set' >>>
s.copy():返回一个新集合。
>>> a {'l', 'e', 'o', 'h'} >>> >>> id(a) 49102280 >>> b = a.copy() >>> id(b) 51347984 >>> del(a) >>> a Traceback (most recent call last): File "<pyshell#112>", line 1, in <module> a NameError: name 'a' is not defined >>> b {'l', 'e', 'o', 'h'} >>>
适用于可变集合的方法：
联合更新（|=）：update() 对原集合进行更新
>>> a= set('hello') >>> a {'l', 'e', 'o', 'h'} >>> b = set('hi') >>> b {'i', 'h'} >>> a |= b >>> a {'l', 'e', 'o', 'i', 'h'} >>> c = frozenset('world') >>> a |= c >>> a {'l', 'w', 'e', 'o', 'i', 'r', 'd', 'h'} >>> c |= a >>> c frozenset({'w', 'o', 'r', 'd', 'l', 'e', 'i', 'h'}) >>> a {'l', 'w', 'e', 'o', 'i', 'r', 'd', 'h'} >>> c.update(a) Traceback (most recent call last): File "<pyshell#64>", line 1, in <module> c.update(a) AttributeError: 'frozenset' object has no attribute 'update'
>>> a
{'i', 'h'}
>>> a.update(c) >>> a {'i', 'h'}
交集更新（&=）：intersection_update()
>>> a {'l', 'w', 'e', 'o', 'i', 'r', 'd', 'h'} >>> b {'i', 'h'} >>> a &= b >>> a {'i', 'h'} >>> c frozenset({'w', 'o', 'r', 'd', 'l', 'e', 'i', 'h'}) >>> a &= c >>> a {'i', 'h'} >>> c &= a >>> c frozenset({'i', 'h'}) >>> a = set('hello') >>> a {'l', 'e', 'o', 'h'} >>> b = set('hi') >>> b {'i', 'h'} >>> a.update(b) >>> a {'l', 'e', 'o', 'i', 'h'} >>> a.intersection_update(b) >>> a {'i', 'h'} >>>
差分更新（-=）：difference_update()
>>> a = set('hello') >>> a {'l', 'e', 'o', 'h'} >>> b =set('hi') >>> b {'i', 'h'} >>> a -= b >>> a {'l', 'e', 'o'} >>> b.difference_update(a) >>> b {'i', 'h'} >>>
^=：symmetric_difference_update()
>>> a = set('hello') >>> a {'l', 'e', 'o', 'h'} >>> b =set('hi') >>> b {'i', 'h'} >>> a ^= b >>> a {'l', 'e', 'o', 'i'} >>> a.symmetric_difference_update(b) >>> a {'l', 'e', 'o', 'h'} >>>