一、定义
set是一个无序且不重复的元素集合。
集合对象是一组无序排列的可哈希的值，集合成员可以做字典中的键。集合支持用in和not in操作符检查成员，由len()内建函数得到集合的基数(大小)， 用 for 循环迭代集合的成员。但是因为集合本身是无序的，不可以为集合创建索引或执行切片(slice)操作，也没有键(keys)可用来获取集合中元素的值。
set和dict一样，只是没有value，相当于dict的key集合，由于dict的key是不重复的，且key是不可变对象因此set也有如下特性：
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不重复
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元素为不可变对象
二、创建
s = set()s = { 11,22,33,44} #注意在创建空集合的时候只能使用s=set()，因为s={}创建的是空字典 a=set('boy')b=set(['y', 'b', 'o','o']) c=set({ "k1":'v1','k2':'v2'}) d={ 'k1','k2','k2'} e={('k1', 'k2','k2')} print(a,type(a)) print(b,type(b)) print(c,type(c)) print(d,type(d)) print(e,type(e)) OUTPUT: { 'o', 'b', 'y'} { 'o', 'b', 'y'} { 'k1', 'k2'} { 'k1', 'k2'} {('k1', 'k2', 'k2')} 三、基本操作
比较
se = { 11, 22, 33}be = { 22, 55} temp1 = se.difference(be) #找到se中存在，be中不存在的集合，返回新值 print(temp1) #{33, 11} print(se) #{33, 11, 22} temp2 = se.difference_update(be) #找到se中存在，be中不存在的集合，覆盖掉se print(temp2) #None print(se) #{33, 11}, 删除
discard()、remove()、pop()
se = { 11, 22, 33}se.discard(11)se.discard(44) # 移除不存的元素不会报错 print(se) se = { 11, 22, 33} se.remove(11) se.remove(44) # 移除不存的元素会报错 print(se) se = { 11, 22, 33} # 移除末尾元素并把移除的元素赋给新值 temp = se.pop() print(temp) # 33 print(se) # {11, 22} 取交集
se = { 11, 22, 33}be = { 22, 55} temp1 = se.intersection(be) #取交集，赋给新值 print(temp1) # 22 print(se) # {11, 22, 33} temp2 = se.intersection_update(be) #取交集并更新自己 print(temp2) # None print(se) # 22 判断
se = { 11, 22, 33}be = { 22}print(se.isdisjoint(be)) #False，判断是否不存在交集（有交集False，无交集True） print(se.issubset(be)) #False，判断se是否是be的子集合 print(se.issuperset(be)) #True，判断se是否是be的父集合 合并
se = { 11, 22, 33}be = { 22}temp1 = se.symmetric_difference(be) # 合并不同项，并赋新值 print(temp1) #{33, 11} print(se) #{33, 11, 22} temp2 = se.symmetric_difference_update(be) # 合并不同项，并更新自己 print(temp2) #None print(se) #{33, 11} 取并集
se = {11, 22, 33}be = {22,44,55}temp=se.union(be) #取并集，并赋新值print(se) #{33, 11, 22}print(temp) #{33, 22, 55, 11, 44} 更新
se = {11, 22, 33}be = {22,44,55}se.update(be) # 把se和be合并，得出的值覆盖seprint(se)se.update([66, 77]) # 可增加迭代项print(se) 集合的转换
se = set(range(4))li = list(se)tu = tuple(se)st = str(se) print(li,type(li)) print(tu,type(tu)) print(st,type(st)) OUTPUT: [0, 1, 2, 3](0, 1, 2, 3) { 0, 1, 2, 3}
四、源码
class set(object): """ set() -> new empty set object set(iterable) -> new set object Build an unordered collection of unique elements. """ def add(self, *args, **kwargs): """添加""" """ Add an element to a set. This has no effect if the element is already present. """ pass def clear(self, *args, **kwargs): """清除""" """ Remove all elements from this set. """ pass def copy(self, *args, **kwargs): """浅拷贝""" """ Return a shallow copy of a set. """ pass def difference(self, *args, **kwargs): """比较""" """ 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): """ Remove all elements of another set from this set. """ pass def discard(self, *args, **kwargs): """删除""" """ Remove an element from a set if it is a member. If the element is not a member, do nothing. """ pass def intersection(self, *args, **kwargs): """ Return the intersection of two sets as a new set. (i.e. all elements that are in both sets.) """ pass def intersection_update(self, *args, **kwargs): """ Update a set with the intersection of itself and another. """ pass def isdisjoint(self, *args, **kwargs): """ Return True if two sets have a null intersection. """ pass def issubset(self, *args, **kwargs): """ Report whether another set contains this set. """ pass def issuperset(self, *args, **kwargs): """ Report whether this set contains another set. """ pass def pop(self, *args, **kwargs): """ Remove and return an arbitrary set element. Raises KeyError if the set is empty. """ pass def remove(self, *args, **kwargs): """ Remove an element from a set; it must be a member. If the element is not a member, raise a KeyError. """ pass def symmetric_difference(self, *args, **kwargs): """ 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): """ Update a set with the symmetric difference of itself and another. """ pass def union(self, *args, **kwargs): """ Return the union of sets as a new set. (i.e. all elements that are in either set.) """ pass def update(self, *args, **kwargs): """ Update a set with the union of itself and others. """ pass def __and__(self, *args, **kwargs): """ Return self&value. """ pass def __contains__(self, y): """ x.__contains__(y) <==> y in x. """ pass def __eq__(self, *args, **kwargs): """ Return self==value. """ pass def __getattribute__(self, *args, **kwargs): """ Return getattr(self, name). """ pass def __ge__(self, *args, **kwargs): """ Return self>=value. """ pass def __gt__(self, *args, **kwargs): """ Return self>value. """ pass def __iand__(self, *args, **kwargs): """ Return self&=value. """ pass def __init__(self, seq=()): # known special case of set.__init__ """ set() -> new empty set object set(iterable) -> new set object Build an unordered collection of unique elements. # (copied from class doc) """ pass def __ior__(self, *args, **kwargs): """ Return self|=value. """ pass def __isub__(self, *args, **kwargs): """ Return self-=value. """ pass def __iter__(self, *args, **kwargs): """ Implement iter(self). """ pass def __ixor__(self, *args, **kwargs): """ Return self^=value. """ pass def __len__(self, *args, **kwargs): """ Return len(self). """ pass def __le__(self, *args, **kwargs): """ Return self<=value. """ pass def __lt__(self, *args, **kwargs): """ Return self