Combine two dictionaries into one in Python

Question

after having carried out unsuccessful research and tests, I have decided to write here. I am trying to merge two dictionaries with the same key into one dictionary by merging the duplicate values. Specifically, I have this code: schools =

firestore.collection('schools').document(regione).collection(provincia).document(comune).collections()
message = []
for collection in schools:
    print(collection.id)
    for doc in collection.stream():
        
        message.append({
            collection.id: {
                doc.id: doc.to_dict()
            }
        })
print(message)
return message

I also tried to insert the return after the for, but it just takes the first value only.

Which as a result gives me:

[
    {
        "Test school": {
            "0": {
                "indirizzo": "Test",
                "INFORMATICA E TELECOMUNICAZIONI": {
                    "3A INF": "G1H8JF"
                }
            }
        }
    },
    {
        "Test School2": {
            "0": {
                "TEST": {
                    "4CCC": "2g45r"
                },
                "indirizzo": "GG1"
            }
        }
    },
    {
        "Test School2": {
            "1": {
                "indirizzo": "gg2",
                "gg": {
                    "asas": "3r3"
                }
            }
        }
    }
]

I want to get this result instead:

{
    {
        "Test School1": {
            "0": {
                "indirizzo": "Test",
                "INFORMATICA E TELECOMUNICAZIONI": {
                    "3A INF": "G1H8JF"
                }
            }
        }
    },
    {
        "Test School2": {
            "0": {
                "TEST": {
                    "4CCC": "2g45r"
                },
                "indirizzo": "GG1"
            },
            "1": {
                  "indirizzo": "gg2",
                  "gg": {
                      "asas": "3r3"
                  }
              }
        }
    }
}

I have tried various codes but I cannot adapt them in my specific case on how to merge the two dictionaries. I hope you can help me out. collection.id contains the name of the school ("Test School1")

doc.id contains the school account ("0")

doc.to_dict() contains the address and all other information

I use Python 3.9.X

I want to clarify that I have also read various answers on this site and I believe that for this specific case it is not a duplicate.

Thanks so much!

Why do you want a list of dictionaries? Wouldn't a single large dictionary make more sense? — Grismar
– Grismar, Commented Feb 16, 2022 at 10:35
I try to get a single dictionary or JSON exactly like in the example I did. — Matteo
– Matteo, Commented Feb 16, 2022 at 10:38
The first example is a list of dictionaries. The second example is two dictionaries side by side. Neither example shows a single dictionary. — Grismar
– Grismar, Commented Feb 16, 2022 at 10:39
I don't know how to explain, I would like to combine Test School 2 -> 0 and Test School 2 -> 1 in one dictionary: { School Test1: { 0: { ... }, 1 { ... } } } — Matteo
– Matteo, Commented Feb 16, 2022 at 10:44
your expected outcome is a set of dicts, which is not valid in python — user7864386
– user7864386, Commented Feb 16, 2022 at 10:44

Grismar · Accepted Answer · 2022-02-16 10:44:24Z

1

The easiest way of keeping track of what you already have somethinf of, is in a dictionary:

from collections import defaultdict

firestore.collection('schools').document(regione).collection(provincia).document(comune).collections()
message = defaultdict(dict)
for collection in schools:
    print(collection.id)
    for doc in collection.stream():
        message[collection.id][doc.id] = doc.to_dict()
print(message)
return message

If you need everything to be split up in multiple dictionaries, you can then break it up afterwards:

final_result = [{school: d} for school, d in message.items()]

answered Feb 16, 2022 at 10:44

Grismar

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1 Comment

Grismar Over a year ago

You're welcome - just FYI: the reason you were getting confusing comments was that you put {} around two dictionaries, but didn't provide any keys. If you remove the {} around the two inner dicts, it becomes a single dict - I didn't catch the outer {} at first (if they were even there), but @enke correctly remarked that what you wrote was effectively a set of two dicts (which can't work, since a dict is not 'hashable'). The confusion arises from {1, 2} being a set and {1: 2} being a dict, both using {} in their literal form.

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