集合
python的set 和其它语言类似，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。
优点：
访问速度快
天生解决了重复问题
例子：
>>> s = set([1,2,3,4]) #创建一个数值集合 >>> s set([1, 2, 3, 4]) >>> t = set("Hello") #创建一个唯一字符的集合 与列表和元组不同，集合是无序的，也无法通过数字进行索引，而且集合里面的元素不能重复 >>> t set(['H', 'e', 'l', 'o']) #发现只出现了一个l >>> a=t|s #t 和s 的并集 >>> a set([1, 2, 3, 'e', 'H', 'l', 'o', 4]) >>> b=t&s #t 和s 的交集 >>> b set([]) >>> c=t - s #求差集(在t，不在s) >>> c set(['H', 'e', 'l', 'o']) >>> d = t ^ s #对称差集(在t或s中，但不会同事出现在二者中) >>> d set([1, 2, 3, 4, 'H', 'l', 'o', 'e']) >>> t set(['H', 'e', 'l', 'o']) ###基本操作 >>> t.add('a') #添加一项 >>> t set(['a', 'H', 'e', 'l', 'o']) >>> s set([1, 2, 3, 4]) >>> s.update([90,34,53]) #在s中添加多项 >>> s set([1, 34, 3, 4, 2, 53, 90]) >>> t set(['a', 'H', 'e', 'l', 'o']) >>> t.remove('e') #删除 >>> t set(['a', 'H', 'l', 'o']) >>> len(s) #set的长度 7 >>> len(t) #set 的长度 4 >>> 53 in s #测试x是否是s的成员 True >>> 2 in s #测试x是否是s的成员 True >>> 20 in s #测试x是否不是s的成员 False >>> s.discard(90) #如果set中存在“90”元素，则删除 >>> s set([1, 34, 3, 4, 2, 53]) >>> s.pop() #删除并且返回集合中一个不确定的元素，如果集合空，则引发KeyError 1 >>> s set([34, 3, 4, 2, 53]) >>> s.pop() 34 >>> s set([3, 4, 2, 53]) >>> s.pop() 3 >>> s set([4, 2, 53]) >>> s.pop() 4 >>> s set([2, 53]) ##为啥我测试每次都是删第一个元素的呢？ >>> s.clear() #删除集合里的所有元素 >>> s set([]) >>> s=set([1, 34, 3, 4, 2, 53, 90]) >>> s set([1, 34, 3, 4, 2, 53, 90]) >>> t set(['a', 'H', 'l', 'o']) >>> s <= t #测试是否s中的每一个元素都在t中 (s.issubset(t)) False >>> s >= t #测试是否t中的每一个元素都在s中 (s.issuperset(t)) False >>> s.union(t) #返回一个新的set ，包含s和t中的每一个元素(s | t) set(['a', 1, 34, 3, 4, 'H', 2, 'o', 'l', 53, 90]) >>> s.intersection(t) #返回一个新的set，包含s和t中的公共元素(s & t) set([]) >>> s.difference(t) #返回一个新的set，包含s中有但是t中没有的元素(s - t) set([1, 34, 3, 4, 2, 53, 90]) >>> s.symmetric_difference(t) #返回一个新的set，包含s和t中不重复的元素 (s ^ t) set(['a', 1, 34, 3, 4, 'H', 2, 'l', 'o', 53, 90]) >>> new_set=s.copy #返回set的一个浅复制 >>> new_set <built-in method copy of set object at 0x7ffe1dab7ed0>
稍稍记住：
s.union(t) = s | t : s和t的并集
s.intersection(t) = s & t : s和t的交集
s.difference(t) = s - t ：差集(在s，不在t)
s.symmetric_difference(t) = s ^ t ：对称差集(在t或s中，但不会同时出现在二者中，包含s和t中不重复的元素)
二.某些方法例子：
(1)difference、difference_update
def difference(self, *args, **kwargs): # real signature unknown
"""
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.)
"""
pass
def difference_update(self, *args, **kwargs): # real signature unknown
""" 删除当前set中的所有包含在 new set 里的元素 """
""" Remove all elements of another set from this set. """
pass
例子：
>>> s1 set(['hy', 'alex', 'yaobin']) >>> s2 set(['test2', 'hehe', 'hy', 'alex', 'yaobin']) >>> s4=s2.difference(s1) >>> s1 set(['hy', 'alex', 'yaobin']) >>> s2 set(['test2', 'hehe', 'hy', 'alex', 'yaobin']) >>> s4 #生成一个新的集合！ set(['test2', 'hehe']) >>> >>> >>> s1 set(['hy', 'alex', 'yaobin']) >>> s2 set(['test2', 'hehe', 'hy', 'alex', 'yaobin']) >>> s5=s2.difference_update(s1) >>> s1 set(['hy', 'alex', 'yaobin']) >>> s2 #把s1存在s2的元素清了！ set(['test2', 'hehe']) >>> s5 #没有生成新的集合！ >>> print s5 None
(2)intersection、intersection_update
def intersection(self, *args, **kwargs): # real signature unknown
""" 取交集，新创建一个set """
"""
Return the intersection of two or more sets as a new set.
(i.e. elements that are common to all of the sets.)
"""
pass
def intersection_update(self, *args, **kwargs): # real signature unknown
""" 取交集，修改原来set """
""" Update a set with the intersection of itself and another. """
pass
例子：
>>> s1 set(['hy', 'alex', 'yaobin']) >>> s2 set(['alex', 'hy', 'test2', 'hehe', 'yaobin']) >>> s3=s2.intersection(s1) >>> s3 #生成一个新的集合 set(['hy', 'alex', 'yaobin']) >>> >>> >>> s1 set(['hy', 'alex', 'yaobin']) >>> s2 set(['alex', 'hy', 'test2', 'hehe', 'yaobin']) >>> s4=s2.intersection_update(s1) >>> s4 >>> print s4 #没有生成一个新的集合 None >>> s1 set(['hy', 'alex', 'yaobin']) >>> s2 #修改s2 去了！ set(['hy', 'alex', 'yaobin'])
(3)isdisjoint
def isdisjoint(self, *args, **kwargs): # real signature unknown
""" 如果没有交集，返回true """
""" Return True if two sets have a null intersection. """
pass
例子：
>>> s1 set(['hy', 'alex', 'yaobin']) >>> s2 set(['hy', 'alex', 'yaobin']) >>> s1.isdisjoint(s2) False >>> s2=set(['a','b','c']) >>> s1.isdisjoint(s2) True
(4)issubset、issuperset
def issubset(self, *args, **kwargs): # real signature unknown
""" 是否是子集 """
""" Report whether another set contains this set. """
pass
def issuperset(self, *args, **kwargs): # real signature unknown
""" 是否是父集 """
""" Report whether this set contains another set. """
pass
例子：
>>> s1 set(['hy', 'alex', 'yaobin']) >>> s2 set(['haha', 'hy', 'alex', 'hehe', 'yaobin']) >>> s1.issubset(s2) True >>> >>> >>> s2.issuperset(s1) True
(5)pop、remove
def pop(self, *args, **kwargs): # real signature unknown
""" 移除 """
"""
Remove and return an arbitrary set element.
Raises KeyError if the set is empty.
"""
pass
def remove(self, *args, **kwargs): # real signature unknown
""" 移除 """
"""
Remove an element from a set; it must be a member.
If the element is not a member, raise a KeyError.
"""
pass
例子：
>>> s1 set(['hy', 'alex', 'yaobin']) >>> s2 set(['haha', 'hy', 'alex', 'hehe', 'yaobin']) >>> s2.pop() #pop可以拿一个元素，可以赋值给你定义的xxx 'haha' >>> s2 set(['hy', 'alex', 'hehe', 'yaobin']) >>> s2.remove() Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: remove() takes exactly one argument (0 given) >>> s2.remove('hy') #要指定元素 >>> s2 set(['alex', 'hehe', 'yaobin'])
(6)symmetric_difference、symmetric_difference_update
def symmetric_difference(self, *args, **kwargs): # real signature unknown
""" 对称差集，创建新对象"""
"""
Return the symmetric difference of two sets as a new set.
(i.e. all elements that are in exactly one of the sets.)
"""
pass
def symmetric_difference_update(self, *args, **kwargs): # real signature unknown
""" 对称差集，改变原来 """
""" Update a set with the symmetric difference of itself and another. """
pass
例子：
>>> s1 set(['hehe', 'hy', 'alex']) >>> s2 set(['hehe', 'yaobin']) >>> s2.symmetric_difference(s1) set(['alex', 'hy', 'yaobin']) >>> s1 set(['hehe', 'hy', 'alex']) >>> s2 #没变 set(['hehe', 'yaobin']) >>> >>> >>> s2.symmetric_difference_update(s1) >>> s1 set(['hehe', 'hy', 'alex']) >>> s2 #变了 set(['hy', 'alex', 'yaobin']) >>>
(7) difference、symetric_difference
def difference(self, *args, **kwargs): # real signature unknown
"""
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.)
"""
pass
def symmetric_difference(self, *args, **kwargs): # real signature unknown
""" 对称差集，创建新对象"""
"""
Return the symmetric difference of two sets as a new set.
(i.e. all elements that are in exactly one of the sets.)
"""
pass
例子：
s1 = set([11,22,33]) s2 = set([22,44]) ret1 = s1.difference(s2) ret2 = s1.symmetric_difference(s2) print ret1 print ret2 结果： set([33, 11]) set([33, 11, 44]) 解析： 可以理解为：ret1，先循环s1，判断不在s2的 ret2，先循环s1，判断不在s2的，后循环s2，判断不在s1的
end