小练习

下列两个字典，使用set得出需要修改（交集）、需要删除（差集）、需要添加的内容。

old_dict = {    "#1":{'hostname':'c1', 'cpu': 2, 'dimm':2048},    "#2":{'hostname':'c2', 'cpu': 2, 'dimm':2048},    "#3":{'hostname':'c3', 'cpu': 2, 'dimm':2048},}new_dict = {    "#1":{'hostname':'c1', 'cpu': 2, 'dimm':4096},    "#3":{'hostname':'c3', 'cpu': 2, 'dimm':2048},    "#4":{'hostname':'c4', 'cpu': 2, 'dimm':2048},}#只对keys作比较，得到所有keys的列表，并转为set集合old_list = set(old_dict.keys())new_list = set(new_dict.keys())#需要更新的内容（交集）update_set  = old_list .intersection(new_list)#需要删除的内容（差集）delete_set = old_list.difference(update_set)#需要添加的内容add_set = new_list.difference(update_set)print(update_set)print(delete_set)print(add_set)

运行结果：

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

图解：

 

set中difference和symmetric_difference的区别

例：

s1 = set([11,22,33])s2 = set([33,44])ret1 = s1.difference(s2)ret2 = s1.symmetric_difference(s2)print(ret1)print(ret2)

运行结果：

{11, 22}{11, 44, 22}

说明：

ret1中只循环s1 ret2中先循环s1,然后循环s2