set使用方法

set 添加一个无序的，用set方法，访问速度快，天生解决了重复问题

1、difference 指定某个元素从原来set取出，并生成新的set

 #difference
 a = set(["aaa","bbb","ccc","aaa"])
 print(a)
 b = a.difference(["aaa"])
 print(b)

 {'ccc', 'bbb', 'aaa'}
 {'ccc', 'bbb'}

2、difference_update 删除原来set里某个元素

 1 #difference_update
 2 a = set(["aaa","bbb","ccc","aaa"])
 3 print(a)
 4 b = a.difference_update(["aaa"])
 5 print(a)
 6 print(b)
 7
 8
 9 {'bbb', 'ccc', 'aaa'}
10 {'bbb', 'ccc'}
11 None

3、pop 删除某个元素

 #pop
 a = set(["aaa","bbb","ccc","aaa"])
 print(a)
 b = a.pop()
 print(a)
 print(b)

 {'aaa', 'bbb', 'ccc'}
 {'bbb', 'ccc'}
 aaa

4、remove 删除指定元素

 #remove
 a = set(["aaa","bbb","ccc","aaa"])
 print(a)
 b = a.remove("ccc")
 print(a)
 print(b)

 {'bbb', 'ccc', 'aaa'}
 {'bbb', 'aaa'}
 None

这里举一个例子，更新、删除、添加原来的表

 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}
 }

 a = set(old_dict.keys())
 b = set(new_dict.keys())

 #要更新的数据
 update_set = a.intersection(b)
 print(update_set)
 #要删除的数据
 delete_set = a.symmetric_difference(update_set)
 print(delete_set)
 #要添加的数据
 add_set = b.symmetric_difference(update_set)
 print(add_set)

 {'#3', '#1'}
 {'#2'}
 {'#4'}

set简单说明：

   1 class set(object):
   2     """
   3     set() -> new empty set object
   4     set(iterable) -> new set object
   5
   6     Build an unordered collection of unique elements.
   7     """
   8     def add(self, *args, **kwargs): # real signature unknown
   9         """
  10         Add an element to a set，添加元素
  11
  12         This has no effect if the element is already present.
  13         """
  14         pass
  15
  16     def clear(self, *args, **kwargs): # real signature unknown
  17         """ Remove all elements from this set. 清除内容"""
  18         pass
  19
  20     def copy(self, *args, **kwargs): # real signature unknown
  21         """ Return a shallow copy of a set. 浅拷贝  """
  22         pass
  23
  24     def difference(self, *args, **kwargs): # real signature unknown
  25         """
  26         Return the difference of two or more sets as a new set. A中存在，B中不存在
  27
  28         (i.e. all elements that are in this set but not the others.)
  29         """
  30         pass
  31
  32     def difference_update(self, *args, **kwargs): # real signature unknown
  33         """ 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"""
  34         pass
  35
  36     def discard(self, *args, **kwargs): # real signature unknown
  37         """
  38         Remove an element from a set if it is a member.
  39
  40         If the element is not a member, do nothing. 移除指定元素，不存在不保错
  41         """
  42         pass
  43
  44     def intersection(self, *args, **kwargs): # real signature unknown
  45         """
  46         Return the intersection of two sets as a new set. 交集
  47
  48         (i.e. all elements that are in both sets.)
  49         """
  50         pass
  51
  52     def intersection_update(self, *args, **kwargs): # real signature unknown
  53         """ Update a set with the intersection of itself and another.  取交集并更更新到A中 """
  54         pass
  55
  56     def isdisjoint(self, *args, **kwargs): # real signature unknown
  57         """ Return True if two sets have a null intersection.  如果没有交集，返回True，否则返回False"""
  58         pass
  59
  60     def issubset(self, *args, **kwargs): # real signature unknown
  61         """ Report whether another set contains this set.  是否是子序列"""
  62         pass
  63
  64     def issuperset(self, *args, **kwargs): # real signature unknown
  65         """ Report whether this set contains another set. 是否是父序列"""
  66         pass
  67
  68     def pop(self, *args, **kwargs): # real signature unknown
  69         """
  70         Remove and return an arbitrary set element.
  71         Raises KeyError if the set is empty. 移除元素
  72         """
  73         pass
  74
  75     def remove(self, *args, **kwargs): # real signature unknown
  76         """
  77         Remove an element from a set; it must be a member.
  78
  79         If the element is not a member, raise a KeyError. 移除指定元素，不存在保错
  80         """
  81         pass
  82
  83     def symmetric_difference(self, *args, **kwargs): # real signature unknown
  84         """
  85         Return the symmetric difference of two sets as a new set.  对称差集
  86
  87         (i.e. all elements that are in exactly one of the sets.)
  88         """
  89         pass
  90
  91     def symmetric_difference_update(self, *args, **kwargs): # real signature unknown
  92         """ Update a set with the symmetric difference of itself and another. 对称差集，并更新到a中 """
  93         pass
  94
  95     def union(self, *args, **kwargs): # real signature unknown
  96         """
  97         Return the union of sets as a new set.  并集
  98
  99         (i.e. all elements that are in either set.)
 100         """
 101         pass
 102
 103     def update(self, *args, **kwargs): # real signature unknown
 104         """ Update a set with the union of itself and others. 更新 """
 105         pass