从python中的最小迭代中获取另一个列表中的列表

Question

I have a list (Let A) which contains list of object and each object contains attribute say name and id and id values are stored in database.In a particular position I have list (Let B) of IDs now i want those objects in list 'A' which have ids in list 'B'.
by using simple iteration i can get those objects from list A.(It may cause more iteration) I want to reduce the iteration as my both lists have more than 1000 of values in each

for clildB in B:
            for childA in A:
                #   MYCODE

Answer 1

To convert your O(n*m) (quadratic) code to O(n+m) (linear):

ids = set(B)
L = [obj for obj in A if obj.id in ids]

item in a_set operation has O(1) (constant) time complexity (average case) , where a_set is a set. Compare it with item in a_list that has O(n) time complexity, where a_list is a list.

Answer 2

idADic = {o['id']:o for o in A}
[idADic.get(o['id']) for o in B]