How to merge dictionaries within two lists if they have a common key-value pair?

Question

I have two lists of dictionaries. Each dictionary in each list has an id field. I'd like to merge the dictionaries in List 1 with the dictionaries in List 2, only if they share a common 'id'

L1 = [{'id':'123','field1':'abc','field2':'def','field3':'ghi'},{'id':'456','field1':'jkl','field2':'mno','field3':'pqr'},{'id':'789','field1':'stu','field2':'vwx','field3':'yz'}] 
L2 = [{'field4':'aaa','field5':'bbb','field6':'ccc','field7':'ddd','id':'101'},{'field4':'eee','field5':'fff','field6':'ggg','field7':'hhh','id':'789'},{'field4':'iii','field5':'jjj','field6':'kkk','field7':'lll','id':'456'},{'field4':'mmm','field5':'nnn','field6':'ooo','field7':'ppp','id':'123'}]


DesiredList = [{'id':'123','field1':'abc','field2':'def','field3':'ghi','field4':'mmm','field5':'nnn','field6':'ooo','field7':'ppp'},{'id':'456','field1':'jkl','field2':'mno','field3':'pqr','field4':'iii','field5':'jjj','field6':'kkk','field7':'lll'},{'id':'789','field1':'stu','field2':'vwx','field3':'yz','field4':'eee','field5':'fff','field6':'ggg','field7':'hhh'},{'field4':'aaa','field5':'bbb','field6':'ccc','field7':'ddd','id':'101'}]

I've done

DesiredList = []
for Dict2 in L2:
    for Dict1 in L1:
        if Dict1['id'] == Dict2['id']:
            Dict2.update(Dict1)
    DesiredList.append(Dict2)

This results in

  >>>DesiredList 
  DesiredList = [{'id': '101', 'field6': 'ccc', 'field7': 'ddd', 'field4': 'aaa', 'field5': 'bbb'}, {'field2': 'vwx', 'field3': 'yz', 'field1': 'stu', 'field6': 'ggg', 'field7': 'hhh', 'field4': 'eee', 'field5': 'fff', 'id': '789'}, {'field2': 'mno', 'field3': 'pqr', 'field1': 'jkl', 'field6': 'kkk', 'field7': 'lll', 'field4': 'iii', 'field5': 'jjj', 'id': '456'}, {'field2': 'def', 'field3': 'ghi', 'field1': 'abc', 'field6': 'ooo', 'field7': 'ppp', 'field4': 'mmm', 'field5': 'nnn', 'id': '123'}]

There must be a better way to do this that is quicker and more efficient.

Answer 1

If you are looking for an efficient way, you could do like this

from itertools import chain
from collections import defaultdict

result = defaultdict(dict)

for c_dict in chain(L1, L2):
    result[c_dict["id"]].update(c_dict)

print result.values()

Output

[{'field1': 'abc',
  'field2': 'def',
  'field3': 'ghi',
  'field4': 'mmm',
  'field5': 'nnn',
  'field6': 'ooo',
  'field7': 'ppp',
  'id': '123'},
 {'field1': 'stu',
  'field2': 'vwx',
  'field3': 'yz',
  'field4': 'eee',
  'field5': 'fff',
  'field6': 'ggg',
  'field7': 'hhh',
  'id': '789'},
 {'field1': 'jkl',
  'field2': 'mno',
  'field3': 'pqr',
  'field4': 'iii',
  'field5': 'jjj',
  'field6': 'kkk',
  'field7': 'lll',
  'id': '456'},
 {'field4': 'aaa',
  'field5': 'bbb',
  'field6': 'ccc',
  'field7': 'ddd',
  'id': '101'}]