python基本数据类型之集合set
一、集合的定义
set集合，是一个无序且不重复的元素集合。
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。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。
二、集合的创建
s = set() s = {11,22,33,44} *注：创建空集合时，只能用set(),如果用第二种方法s={}，创建的实际上是一个空字典。 s = {} print(type(s)) <class 'dict'>
a=set('boy') b=set(['y', 'b', 'o','o']) c=set({"k1":'v1','k2':'v2'}) d={'k1','k2','k2'} e={('k1', 'k2','k2')} print(a,type(a)) print(b,type(b)) print(c,type(c)) print(d,type(d)) print(e,type(e)) 执行结果如下： {'o', 'b', 'y'} <class 'set'> {'o', 'b', 'y'} <class 'set'> {'k1', 'k2'} <class 'set'> {'k1', 'k2'} <class 'set'> {('k1', 'k2', 'k2')} <class 'set'>
三、集合的功能
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. 清楚内容""" 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. 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 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，否则返回False""" 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. 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. 对称交集 (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. 对称交集，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
基本功能：
- 增加
a=set('python') a.add('tina') print(a) b=set('python') b.update('tina') print(b) 执行结果如下： {'tina', 'o', 'p', 'n', 't', 'y', 'h'} {'o', 'i', 'p', 'a', 'n', 't', 'y', 'h'} ################## 由以上代码可以看出，add是单个元素的添加，而update是批量的添加。输出结果是无序的，并非添加到尾部。
- 删除（remove，discard，pop）
c={'p', 'i', 'h', 'n', 'o', 'y', 't'}
c.remove('p')
print(c)
c={'p', 'i', 'h', 'n', 'o', 'y', 't'}
c.discard('p')
print(c)
c={'p', 'i', 'h', 'n', 'o', 'y', 't'}
c.pop()
print(c)
执行结果如下： {'i', 'h', 't', 'o', 'y', 'n'}
#####
当执行c.remove('p','i')和c.discard('p','i')时，报错：TypeError: remove() takes exactly one argument (2 given)，说明remove和discard删除元素时都只能一个一个的删，同add对应。
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remove，pop和discard的区别：
discard删除指定元素，当指定元素不存在时，不报错；
remove删除指定元素，但当指定元素不存在时，报错：KeyError。
pop删除任意元素，并可将移除的元素赋值给一个变量，不能指定元素移除。
- 清空
c={'p', 'i', 'h', 'n', 'o', 'y', 't'}
c.clear()
print(c)
执行结果如下：
set()
set的特有功能：
s1 = {0} s2 = {i % 2 for i in range(10)} s = set('hi') t = set(['h', 'e', 'l', 'l', 'o']) print(s.intersection(t), s & t) # 交集 print(s.union(t), s | t) # 并集 print(s.difference(t), s - t) # 差集 print(s.symmetric_difference(t), s ^ t) # 对称差集 print(s1.issubset(s2), s1 <= s2) # 子集（被包含） print(s1.issuperset(s2), s1 >= s2) # 父集（包含） 执行结果如下： {'h'} {'h'} {'i', 'e', 'h', 'l', 'o'} {'i', 'e', 'h', 'l', 'o'} {'i'} {'i'} {'e', 'l', 'o', 'i'} {'e', 'l', 'o', 'i'} True True False False
s = {11,22,33}
t = {22,44}
print(s.isdisjoint(t))#（disjoint脱节的，）即如果没有交集，返回True，否则返回False
s.difference_update(t)#将差集覆盖到源集合，即从当前集合中删除和B中相同的元素
print(s)
执行结果如下：
False
{33, 11}
s = {11,22,33}
t = {22,44}
s.intersection_update(t)#将交集覆盖到源集合
print(s)
执行结果如下：
{22}
s = {11,22,33}
t = {22,44}
s.symmetric_difference_update(t)#将对称差集覆盖到源集合
print(s)
执行结果如下：
{33, 11, 44}
四、集合的转换
se = set(range(4)) li = list(se) tu = tuple(se) st = str(se) print(li,type(li)) print(tu,type(tu)) print(st,type(st)) 执行结果如下： [0, 1, 2, 3] <class 'list'> (0, 1, 2, 3) <class 'tuple'> {0, 1, 2, 3} <class 'str'>
五、练习题
寻找差异：哪些需要删除？哪些需要新建？哪些需要更新？
# 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 }
}
注意：无需考虑内部元素是否改变，只要原来存在，新汇报也存在，就是需要更新
del_dict = set(old_dict).difference(set(new_dict)) add_dict = set(new_dict).difference(set(old_dict)) update_dict = set(new_dict).intersection(set(old_dict)) print(del_dict) print(add_dict) print(update_dict) 执行结果如下： {'#2'} {'#4'} {'#3', '#1'}
#!/usr/bin/python # -*- coding:utf-8 -*- 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}, } 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}, } new_set = set() old_set = set() for i in new_dict: new_set.add(i) for j in old_dict: old_set.add(j) new_add = new_set.difference(old_set) #new_dict中有，old_dict中沒有 old_del = old_set.difference(new_set) #old_dict中有，new_dict中沒有 update = new_set.intersection(old_set) #old_dict和new_dict共同有的，需要把new_dict更新到old_dict中 for k in new_add: old_dict[k] = new_dict[k] #將new_dict中新增的內容添加到old_dict中 for v in old_del: del old_dict[v] #將old_dict中失效的內容刪除 for m in update: old_dict[m] = new_dict[m] #把new_dict更新到old_dict中 print(old_dict)
