How do I add information to an existing json file using python?

Question

I’m trying to create a function to save data in a json file in python and I can’t do it without the old data being overwritten by the new ones (I want the old ones to remain and the new ones to be added soon after).

Nor can I keep the old data together with the new data without json becoming invalid, since "a" mode does not add a comma after the first object before adding the new one...

I’ve been trying to do as I’ve seen in some places: upload the json file, add new content and save it again in the file, but I’m not able to build the function without error.

my function is so with the suggestions of the comments:

def salvar_dados(nomedojson, file):
    if not isfile(nomedojson):  # Verifica se o arquivo já existe, se não existir ele vai criar
        with open(nomedojson, "w", encoding="utf-8") as dados:
            lista = []
            lista.append(file)
            salvando1 = json.dump(lista, dados, indent=2, separators=(",", ": "), sort_keys=True)
            return salvando1
    else:  # condição que atesta que o arquivo já existe e só precisa ser atualizado
        with open(nomedojson, "r+", encoding="utf-8") as dados:
            carregando = [json.load(dados)]  # comando para carregar o arquivo existente
            atualizando = carregando.append(file)  # comando para supostamente atualizar o conteúdo
            salvando2 = json.dump(atualizando, dados, indent=2, separators=(",", ": "), sort_keys=True)
            return salvando2

And the following error appears:

data sample:

 dic_p = {self.nome_completo[0]+" "+self.nome_completo[1]: {'Nome': self.nome[0], 'Sobrenome': self.sobrenome[0]}}

I wanted it to stay that way:

(I inserted by hand just to show, I can’t leave this way running the code)

But you’re getting that way:

I’ve been trying to solve this problem for 3 days, I’m running out of ideas to test... If anyone can help I appreciate!

Answer 1

I want to thank everyone who has devoted a few minutes of their time to help me, today I finally got my code running to save the data the way I need it. So, not to leave future visitors unanswered I will tell you my solution:

I reworked the function of loading and saving the files and left them that way:

def salvar_dados(nomedojson, file):
with open(nomedojson, "w", encoding="utf-8") as dados:
    salvando = json.dump(file, dados, indent=2, separators=(",", ": "), sort_keys=True)
    return salvando

def carregar_dados(nomedojson):
if isfile(nomedojson):  # Verifica se o arquivo já existe, se sim, o json será carregado
    with open(nomedojson, "r", encoding="utf-8") as dados:
        return json.load(dados)
else:  # Se o json ainda não existe, a função cria e retorna uma lista
    temporario = []
    return temporario

Then I make the function load the file before the whole program start:

try:
    dados_p = carregar_dados("Banco de dados1.json")
    dados_s = carregar_dados("Banco de dados2.json")
    dados_c = carregar_dados("Banco de dados3.json")
    # Se os jsons ainda não existirem, uma lista para cada um será retornada
except Exception as erro:
    print("Ocorreu um erro durante o carregamento: ", erro)

After loading the jsons (or lists), a main menu appears, where the user can register and query the json files.

A very important detail is to use the same variables "dados_p", "dados_s" and "dados_c" to effect and save changes to json files using the append command. Ex: "dados_p.append(file)"

It took me a long time to learn how to do this kind of thing. I hope that I have been able to be clear in my question and in my answer to the question. Once again, many thanks to those who have dedicated their attention to help me! I hope also to be able to help those with the same problem.