如何合并键上的两个字典列表-Python？

Question

I have two dict lists that I am trying to merge on a unique key but I cannot get my head around how to approach this.

dict 1:

A = {'1': [{'A': 'A_1', 'start': 'S'}, {'A': 'A_2', 'start': 'M'}], 
'2': [{'A': 'A_1', 'start': 'S'}, {'A': 'A_2', 'start': 'M'}]}

dict 2:

B = {'1': [{'l_1': 'www.l_1', 'l_2': 'www.l_2'}], 
'2': [{'l_1': 'www.myl_1', 'l_2': 'www.myl_2'}]}

What I am trying to achieve:

combined = {'1': [{'A': 'A_1', 'start': 'S', 'l_1': 'www.l_1', 'l_2': 'www.l_2'}, {'A': 'A_2', 'start': 'M', 'l_1': 'www.l_1', 'l_2': 'www.l_2'}], 
'2': [{'A': 'A_1', 'start': 'S', 'l_1': 'www.myl_1', 'l_2': 'www.myl_2'}, {'A': 'A_2', 'start': 'M', 'l_1': 'www.myl_1', 'l_2': 'www.myl_2'}]}

Below is the code that I have written so far. But it does not provide me with the desired result..

from itertools import chain
from collections import defaultdict

dict3 = defaultdict(list)
for k, v in chain(A.items(), B.items()):
    dict3[k].append(v)

print(dict3)

Answer 1

You can use itertools.product to merge dict values from corresponding keys and then use Python 3's dict merge syntax:

from itertools import product

dct =  {k: [{**d1, **d2} for d1, d2 in product(v, B[k])] 
                                           for k, v in A.items()}

In Python 2, you can apply a comprehension on the tuples from product, and build a merged dict from the elements:

dct =  {key: [{k: v for d in tup for k, v in d.items()} 
                  for tup in product(val, B[key])] 
                                 for key, val in A.items()}

---

{'1': [{'A': 'A_1', 'l_1': 'www.l_1', 'l_2': 'www.l_2', 'start': 'S'},
       {'A': 'A_2', 'l_1': 'www.l_1', 'l_2': 'www.l_2', 'start': 'M'}],
 '2': [{'A': 'A_1', 'l_1': 'www.myl_1', 'l_2': 'www.myl_2', 'start': 'S'},
       {'A': 'A_2', 'l_1': 'www.myl_1', 'l_2': 'www.myl_2', 'start': 'M'}]}

Answer 2

for i in a:
    if i in b:

        for j in range(min(len(a[i]),len(b[i]))):
            a[i][j]=dict(a[i][j].items()+b[i][j].items()) #re-assign after combining

        if len(b[i])>len(a[i]):       # length case
             for j in range(len(a[i]),len(b[i])):
                  a[i].append(b[i][j])

for i in b:         # if not in a
   if i not in a:
     a[i]=b[i]
print a