通过 python 中的多个键对字典进行分组

Question

{
04-21: {
          a: [1,2,3,4]
          a: [5,6,7]
          b: [8,9]
       }
04-22: {
          a: [1,3,4]
          a: [2,6,7]
          a: [3,8]
          b: [1,4,2]
          b: [8,9]
       }
}

How do I group this dictionary by first and second value to produce:

{
 04-21:{
         a: [1,2,3,4,5,6,7]
         b: [8,9]
       }
 04-22:{
         a: [1,3,4,2,6,7,3,8]
         b: [1,4,2,8,9]
}

Following code gives me error:

for key, group in itertools.groupby(L, lambda x: x[0] ,x[1]): 
    print(key + " :", list(group)) 

Answer 1

As soon as you execute that dictionary in Python ie:

d = {'04-21': {
          'a': [1,2,3,4],
          'a': [5,6,7],
          'b': [8,9]
       },
'04-22': {
          'a': [1,3,4],
          'a': [2,6,7],
          'a': [3,8],
          'b': [1,4,2],
          'b': [8,9]
       }
}

The dictionary becomes:

{'04-21': {'a': [5, 6, 7], 'b': [8, 9]}, '04-22': {'a': [3, 8], 'b': [8, 9]}}