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：
不重复
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. """
pass
def __rsub__(self, *args, **kwargs):
""" Return value-self. """
pass
def __rxor__(self, *args, **kwargs):
""" Return value^self. """
pass
def __sizeof__(self):
""" S.__sizeof__() -> size of S in memory, in bytes """
pass
def __sub__(self, *args, **kwargs):
""" Return self-value. """
pass
def __xor__(self, *args, **kwargs):
""" Return self^value. """
pass
__hash__ = None