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：

1. 不重复

2. 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'} <class 'set'> {'o', 'b', 'y'} <class 'set'> {'k1', 'k2'} <class 'set'> {'k1', 'k2'} <class 'set'> {('k1', 'k2', 'k2')} <class 'set'>

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se
print(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] <class 'list'> (0, 1, 2, 3) <class 'tuple'> {0, 1, 2, 3} <class 'str'>

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<value. """ pass  @staticmethod def __new__(*args, **kwargs): """ Create and return a new object. See help(type) for accurate signature. """ pass def __ne__(self, *args, **kwargs): """ Return self!=value. """ pass def __or__(self, *args, **kwargs): """ Return self|value. """ pass def __rand__(self, *args, **kwargs): """ Return value&self. """ pass def __reduce__(self, *args, **kwargs): """ Return state information for pickling. """ pass def __repr__(self, *args, **kwargs): """ Return repr(self). """ pass def __ror__(self, *args, **kwargs): """ Return value|self. """