一、集合的特点：
1、访问速度快
2、天生解决了重复问题
二、集合的定义方法：
a=set()
b=set(['a','b','c'])
三、集合中的方法：
def add(self, *args, **kwargs): # real signature unknown
"""
Add an element to a set.
This has no effect if the element is already present.
在集合中增加元素
"""
pass
eg：
def clear(self, *args, **kwargs): # real signature unknown
"""
Remove all elements from this set.
清空集合
"""
pass
eg：
def copy(self, *args, **kwargs): # real signature unknown
"""
Return a shallow copy of a set.
集合的浅拷贝
"""
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.)
求两个集合的不同（差集），生成一个新的集合
"""
pass
eg：
def difference_update(self, *args, **kwargs): # real signature unknown
"""
Remove all elements of another set from this set.
求两个集合的不同（差集），改变原来的集合
"""
pass
eg：
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.
移除集合中的一个指定元素，如果这个元素不存在，则不变
"""
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.)
求两个集合的交集，生成一个新的集合
"""
pass
eg：
def intersection_update(self, *args, **kwargs): # real signature unknown
"""
Update a set with the intersection of itself and another.
求两个集合的交集，并改变原集合
"""
pass
eg：
def isdisjoint(self, *args, **kwargs): # real signature unknown
"""
Return True if two sets have a null intersection.
判断两个集合是否没有交集，如果是返回True，如果不是返回False
"""
pass
eg：
def issubset(self, *args, **kwargs): # real signature unknown
"""
Report whether another set contains this set.
判断一个集合是否是另一个集合的子集
"""
pass
eg：
def issuperset(self, *args, **kwargs): # real signature unknown
"""
Report whether this set contains another set.
判断一个集合是否包含另一个集合
"""
pass
eg：
def pop(self, *args, **kwargs): # real signature unknown
"""
Remove and return an arbitrary set element.
Raises KeyError if the set is empty.
弹出集合中的元素
"""
pass
eg：
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.
移除集合中的元素
"""
pass
eg：
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.)
把两个集合中的不同元素放到一个新的集合中
"""
pass
eg：
def symmetric_difference_update(self, *args, **kwargs): # real signature unknown
"""
Update a set with the symmetric difference of itself and another.
两个集合不相同的元素，并改变原集合
"""
pass
eg：
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.)
求两个集合的并集，并生成一个新的集合
"""
pass
eg：
def update(self, *args, **kwargs): # real signature unknown
"""
Update a set with the union of itself and others.
改变原集合
"""
pass
eg：
