014-python基础-set集合

集合是一个无序的，不重复的数据组合，它的主要作用如下：

• 去重，把一个列表变成集合，就自动去重了
• 关系测试，测试两组数据之前的交集、差集、并集等关系

注：作为一个无序的集合，sets不记录元素位置或者插入点。因此sets不支持indexing，slicing(切片）

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.     #添加元素
        
        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. """     #清除所有元素
        pass

    def copy(self, *args, **kwargs): # real signature unknown
        """ Return a shallow copy of a set. """            #浅拷贝
        pass

    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.    移除指定元素，不存在不报错
        
        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.   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.   取交集并更新到a中 """
        pass

    def isdisjoint(self, *args, **kwargs): # real signature unknown
        """ Return True if two sets have a null intersection. 如果没有交集，返回True """
        pass

    def issubset(self, *args, **kwargs): # real signature unknown
        """ Report whether another set contains this set. 是否是子序列  """
        pass

    def issuperset(self, *args, **kwargs): # real signature unknown
        """ Report whether this set contains another set.   是否是父序列"""
        pass

    def pop(self, *args, **kwargs): # real signature unknown
        """
        Remove and return an arbitrary set element.  移除元素
        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.   移除指定元素，不存在保错
        
        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.   对称差集，a有b没有 + b有a没有  
        
        (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，一般把一个list通过迭代方式更新到set集群中"""
        pass

 练习：寻找差异

# 数据库中原有
old_dict = {
    "#1":{ 'hostname':c1, 'cpu_count': 2, 'mem_capicity': 80 },
    "#2":{ 'hostname':c1, 'cpu_count': 2, 'mem_capicity': 80 }
    "#3":{ 'hostname':c1, 'cpu_count': 2, 'mem_capicity': 80 }
}
   
# cmdb 新汇报的数据
new_dict = {
    "#1":{ 'hostname':c1, 'cpu_count': 2, 'mem_capicity': 800 },
    "#3":{ 'hostname':c1, 'cpu_count': 2, 'mem_capicity': 80 }
    "#4":{ 'hostname':c2, 'cpu_count': 2, 'mem_capicity': 80 }
}

old_set = set(old_dict.keys())           #获取数据库中的主键
new_set = set(new_dict.keys())           

remove_set = old_set.difference(new_set)   #数据库中需要删除的集合
add_set = new_set.difference(old_set)      #数据库中需要增加的集合
update_set = old_set.intersection(new_set) #数据库中需要更新的集合