merging several python dictionaries values ("sub"dictionaries)

Question

This is an extension of this question. And this seems to show an example of appending to an array, not adding another value to a sub-dict.

dict_1 = {a: {price: 4000}, b: {price: 14000} }

dict_2 = {a: {discount: 0100}, b: {discount: 0400} }

dict_3 = {a: {amount: 41}, b: {amount: 522} }

I would like to merge them to be:

merged_dict: { a: {
                   price: 4000, 
                   discount: 0100,
                   amount: 41
                  }, 
               b: {
                   price: 14000, 
                   discount: 0400,
                   amount: 522
               } 
              }

How to achieve that? And how would that be if there was en even longer list of dictionaries to merge? The dictionaries will always have the same keys (a, b).

I tried doing the same as in the first hyperlink but the .items() seem to make it unscalable.

What was the difficulty when you tried to do this? Have you tried writing something like: `for k in dict_1: merged_dict[k]['price'] = dict_1[k]['price']; for k in dict_2: merged_dict[k]['discount'] = dict_2[k]['discount']`, etc.? — mkrieger1, Feb 19 '21 at 19:29
I also don't understand what is the difference between this question and your earlier question you've linked, other than here you are showing 3 input dictionaries instead of 2. — mkrieger1, Feb 19 '21 at 19:43
```merged_dict = {k: { **dict_1[k], **dict_2[k] } for k in dict_2.keys()}``` this has two dictionaries, and loops over the keys of the second dict only. I can't think of how to do this, since which dict should I iterate over? — uber, Feb 19 '21 at 19:45

score 1 · Accepted Answer · answered Feb 19 '21 at 21:10

You can generalize this kind of merge by placing your dictionaries in a list and creating the merged dictionary in a comprehension:

dict_1 = {"a": {"price": 4000}, "b": {"price": 14000} }

dict_2 = {"a": {"discount": 100}, "b": {"discount": 400} }

dict_3 = {"a": {"amount": 41}, "b": {"amount": 522} }

dicts  = [dict_1, dict_2, dict_3]

merged = { k:dict(kv for d in dicts for kv in d[k].items()) for k in dicts[0] }

print(merged)
{'a': {'price': 4000, 'discount': 100, 'amount': 41}, 
 'b': {'price': 14000, 'discount': 400, 'amount': 522}}

merging several python dictionaries values ("sub"dictionaries)

1 Answers1