集合

set
创建空集合  a=set()
转化一个数据为集合：set（obj）,  注意数字不能直接转化成集合，其他都可以，只要是可迭代类型
set（一个字典），则集合内元素为字典的键值：
关键是集合内置了去重，交集，并集，差集，对称差集函数，这是别的数据类型没有的
def difference(self, *args, **kwargs): # real signature unknown
  """
  Return the difference of two or more sets as a new set. A中存在，B中不存在
         
  (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.  从当前集合中删除和B中相同的元素"""
　　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. 移除指定元素，不存在不保错
  """
  pass
 
def intersection(self, *args, **kwargs): # real signature unknown
    """
  Return the intersection of two sets as a new set. 交集
         
  (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.  取交集并更更新到A中 """
  pass
 
def pop(self, *args, **kwargs): # real signature unknown
  """
  Remove and return an arbitrary set element.
  Raises KeyError if the set is empty. 移除元素
  """
  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. 移除指定元素，不存在保错
  """
  pass
 
def symmetric_difference(self, *args, **kwargs): # real signature unknown
  """
  Return the symmetric difference of two sets as a new set.  对称差集，所有差集，A中有B中没有+B中有A中没
         
  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. 对称差集，并更新到a中 """
  pass
 
def union(self, *args, **kwargs): # real signature unknown
  """
  Return the union of sets as a new set.  并集
         
  (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. 更新 """
  pass
 
实例：
　　