Python set集合
一、 set集合概述
①set集合，是一个无序且不重复的元素集合。
②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。
③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。
④集合set是Python中一种基本数据类型，它分为可变集合（set）和不可变集合（frozenset）两种。
二、set的操作
1. set的创建
集合中set括号中需要的参数的数据类型有：序列（包括字符串、列表、元组），字典或者是另一个集合，但是不能是数值类型，如int类型。
s1=() #创建空集合set()
print(s1)
s2=set(['carlos','alex','eric','tony']) #列表做参数
print(s2)
s3=set('carlos')#字符串做参数
print(s3)
s4=set((1,2,3))#元组做参数
print(s4)
s5=set({'name':'carlos','age':'26'})#元组做参数 , 只取值字典中的key
print(s5)
输出
()
{'tony', 'carlos', 'alex', 'eric'}
{'l', 'o', 'a', 's', 'r', 'c'}
{1, 2, 3}
{'age', 'name'}
s=set(['carlos','alex','eric','tony','carlos']) #set中的元素是无序不重复 的，可以利用这个特点去除列表中的重复元素
print(s)
输出
{'alex', 'carlos', 'tony', 'eric'}
2. set集合的添加
2.1 add(self, *args, **kwargs)把要传入的元素作为一个整体添加到集合中
s=set(['carlos','alex','eric','tony'])
print(s)
s.add('gary')
print(s)
输出
{'tony', 'carlos', 'alex', 'eric'}
{'tony', 'alex', 'gary', 'eric', 'carlos'}
2.2 update(self, *args, **kwargs) 要传入的元素拆分成单个字符，存于集合中，并去掉重复的字符
s=set(['carlos','alex','eric','tony'])
print(s)
s.update('amy')
print(s)
输出
{'tony', 'carlos', 'alex', 'eric'}
{'a', 'm', 'eric', 'tony', 'y', 'carlos', 'alex', 'gary'}
3.集合的删除
集合的删除操作使用的方法跟列表是一样的，使用的也是remove方法，若不存在，报错
s=set(['carlos','alex','eric','tony'])
print(s)
s.remove('alex')
print(s)
输出
{'tony', 'eric', 'alex', 'carlos'}
{'tony', 'eric', 'carlos'}
4. 集合的遍历
s=set(['carlos','alex','eric','tony'])
for i in s:
print(i)
输出
tony
eric
alex
carlos
s=set(['carlos','alex','eric','tony'])
for idx, i in enumerate(s) :
print(idx,i)
输出
0 tony
1 alex
2 eric
3 carlos
三、集合的一些操作符
1.交集 python中求集合的交集使用的符号是“&”，返回连个集合的共同元素的集合，即集合的交集。
s1=set('carlos')
print(s1)
s2=set('alex')
print(s2)
s=s1&s2
print(s)
输出
{'o', 's', 'r', 'c', 'l', 'a'}
{'x', 'l', 'a', 'e'}
{'l', 'a'}
2.并集（合集） Python中求集合的并集用的是符号“|”，返回的是两个集合所有的并去掉重复的元素的集合。
s1=set('carlos')
print(s1)
s2=set('alex')
print(s2)
s=s1|s2
print(s)
输出
{'s', 'r', 'c', 'o', 'l', 'a'}
{'e', 'l', 'a', 'x'}
{'s', 'x', 'r', 'c', 'o', 'e', 'l', 'a'}
3.差集 Python中差集使用的符号是减号“-” ，返回的结果是在集合st1中但不在集合s2中的元素的集合
s1=set('carlos')
print(s1)
s2=set('alex')
print(s2)
s=s1-s2
print(s)
输出
{'l', 's', 'r', 'a', 'c', 'o'}
{'a', 'l', 'x', 'e'}
{'r', 'c', 's', 'o'}
4.查看两个集合的不同之处，使用的difference函数，等价于差集
不同指的是集合s3相对于集合s1，不同的地方，也就是所有在集合s1中，而不再集合s2中的的元素组成的新集合。
s1=set('carlos')
s2=set('alex')
s=s1-s2
s3=s1.difference(s2)
print(s)
print(s3)
输出
{'r', 'o', 'c', 's'}
{'r', 'o', 'c', 's'}
5. 集合的范围判断
集合可以使用大于（>）、小于（<）、大于等于（>=）、小于等于（<=）、等于（==）、不等于（！=）来判断某个集 合是否完全包含于另一个集合，也可以使用子父集判断函数。 返回值为True 或者False。
6. 集合的成员运算符 使用成员运算符，in和not in，判断某个对象是否是集合中的成员
s1=([1,2,3,4,5,])
result=1 in s1
print(result)
result=4 not in s1
print(result)
输出
True
False
7. 求集合的长度 使用len()函数
s1=([1,2,3,4,5,])
result=len(s1)
print(result)
输出 5
四、set的方法
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): # real signature unknown
"""
Add an element to a set. This has no effect if the element is already present.
"""
pass def clear(self, *args, **kwargs): # real signature unknown
""" Remove all elements from this set. """
pass def copy(self, *args, **kwargs): # real signature unknown
""" Return a shallow copy of a set. """
pass 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
""" Remove all elements of another set from this set. """
pass def discard(self, *args, **kwargs): # real signature unknown
"""
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): # real signature unknown
"""
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): # real signature unknown
""" Update a set with the intersection of itself and another. """
pass def isdisjoint(self, *args, **kwargs): # real signature unknown
""" Return True if two sets have a null intersection. """
pass def issubset(self, *args, **kwargs): # real signature unknown
""" Report whether another set contains this set. """
pass def issuperset(self, *args, **kwargs): # real signature unknown
""" Report whether this set contains another set. """
pass def pop(self, *args, **kwargs): # real signature unknown
"""
Remove and return an arbitrary set element.
Raises KeyError if the set is empty.
"""
pass def remove(self, *args, **kwargs): # real signature unknown
"""
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): # real signature unknown
"""
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
""" Update a set with the symmetric difference of itself and another. """
pass def union(self, *args, **kwargs): # real signature unknown
"""
Return the union of sets as a new set. (i.e. all elements that are in either set.)
"""
pass def update(self, *args, **kwargs): # real signature unknown
""" Update a set with the union of itself and others. """
pass def __and__(self, *args, **kwargs): # real signature unknown
""" Return self&value. """
pass def __contains__(self, y): # real signature unknown; restored from __doc__
""" x.__contains__(y) <==> y in x. """
pass def __eq__(self, *args, **kwargs): # real signature unknown
""" Return self==value. """
pass def __getattribute__(self, *args, **kwargs): # real signature unknown
""" Return getattr(self, name). """
pass def __ge__(self, *args, **kwargs): # real signature unknown
""" Return self>=value. """
pass def __gt__(self, *args, **kwargs): # real signature unknown
""" Return self>value. """
pass def __iand__(self, *args, **kwargs): # real signature unknown
""" 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): # real signature unknown
""" Return self|=value. """
pass def __isub__(self, *args, **kwargs): # real signature unknown
""" Return self-=value. """
pass def __iter__(self, *args, **kwargs): # real signature unknown
""" Implement iter(self). """
pass def __ixor__(self, *args, **kwargs): # real signature unknown
""" Return self^=value. """
pass def __len__(self, *args, **kwargs): # real signature unknown
""" Return len(self). """
pass def __le__(self, *args, **kwargs): # real signature unknown
""" Return self<=value. """
pass def __lt__(self, *args, **kwargs): # real signature unknown
""" Return self<value. """
pass @staticmethod # known case of __new__
def __new__(*args, **kwargs): # real signature unknown
""" Create and return a new object. See help(type) for accurate signature. """
pass def __ne__(self, *args, **kwargs): # real signature unknown
""" Return self!=value. """
pass def __or__(self, *args, **kwargs): # real signature unknown
""" Return self|value. """
pass def __rand__(self, *args, **kwargs): # real signature unknown
""" Return value&self. """
pass def __reduce__(self, *args, **kwargs): # real signature unknown
""" Return state information for pickling. """
pass def __repr__(self, *args, **kwargs): # real signature unknown
""" Return repr(self). """
pass def __ror__(self, *args, **kwargs): # real signature unknown
""" Return value|self. """
pass def __rsub__(self, *args, **kwargs): # real signature unknown
""" Return value-self. """
pass def __rxor__(self, *args, **kwargs): # real signature unknown
""" Return value^self. """
pass def __sizeof__(self): # real signature unknown; restored from __doc__
""" S.__sizeof__() -> size of S in memory, in bytes """
pass def __sub__(self, *args, **kwargs): # real signature unknown
""" Return self-value. """
pass def __xor__(self, *args, **kwargs): # real signature unknown
""" Return self^value. """
pass __hash__ = None
set源码
1、add(self, *args, **kwargs) 将元素 添加到集合s中，若重复则不进行任何操作
update(self, *args, **kwargs) 将集合 x 并入原集合s中，x 还可以是列表，元组，字典等，x 可以有多个，用逗号分开
2、clear(self, *args, **kwargs) 删除 set 中的所有元素
3、copy(self, *args, **kwargs) 复制集合
4、difference(self, *args, **kwargs) 返回一个新的 set 包含 s1中有但是s2中没有的元素（生成新集合，不改变原集合）
difference_update(self, *args, **kwargs) 返回一个新的 set 包含 s1和 s2中不重复的元素（改变原集合）
s1=set('carlosalexamy')
s2=set('alextong')
s3=s1.difference(s2)
s4=s1.difference_update(s3)
print(s3)
print(s4)
输出
{'s', 'c', 'm', 'r', 'y'}
None
5、discard(self, *args, **kwargs) 如果在 set “s”中存在元素 x, 则删除。若不存在，不会引发错误
s1=set(['carlos','alex','eric','tony'])
s1.discard('tony')
print(s1)
输出{'carlos', 'alex', 'eric'}
6、intersection(self, *args, **kwargs) 取交集，新建一个set
intersection_update(self, *args, **kwargs) 取交集，修改原来set
7. isdisjoint(self, *args, **kwargs) 如果没有交集，返回Ture
8. issubset(self, *args, **kwargs) 是否是子集
9. issuperset(self, *args, **kwargs) 是否是父集
10. pop(self, *args, **kwargs) 删除并且返回 set “s”中的一个不确定的元素, 如果为空则引发 KeyError （在原集合拿走一个随机元素，并得到这个元素， 这个是两个动作）
s1=set(['carlos','alex','eric','tony'])
result=s1.pop()
print(s1)
print(result)
输出
{'carlos', 'tony', 'alex'}
eric
11. remove(self, *args, **kwargs) 从 set “s”中删除元素 x, 如果不存在则引发 KeyError（在原集合拿走一个指定元素，无返回值）
s1=set(['carlos','alex','eric','tony'])
result=s1.remove('alex')
print(s1)
print(result)
输出
{'carlos', 'tony', 'eric'}
None
12. symmetric_difference(self, *args, **kwargs) 取差集，新建一个set
symmetric_difference_update(self, *args, **kwargs) 取差集，改变原来set
13. union(self, *args, **kwargs) 取并集
五、 举例子