Append list in JSON file with Python

Question

I'm trying to append a list with new names in a json file.

JSON structure:

{
    "users": [
        "User1",
        "User2",
        "User3"
    ]
}

I have tried this:

with open('data/users.json', 'r') as json_file:
    json_data = json.load(json_file)
    user_list = json_data["users"]
 with open('data/users.json', 'w') as json_file:
    user_list.append(name)
    json.dump(user_list, json_file)

But it turns out like this:

["User1", "User2", "User3", "User4"]

Why and how do I fix it?

You're dumping the wrong thing: json.dump(json_data, json_file) — cs95
– cs95, Commented Mar 14, 2018 at 22:00
Is it because you are adding the data as a list, whereas the JSON data is more like a dictionary? — Adriano
– Adriano, Commented Mar 14, 2018 at 22:02
@Adriano There can be just as many lists as dictionaries in JSON, they just make accessing the data more cumbersome. But that doesn't in itself make them any less valid. — roganjosh
– roganjosh, Commented Mar 14, 2018 at 22:06

Brendan Abel · Accepted Answer · 2018-03-15 19:48:25Z

3

You need to write the whole data dictionary, not just the list

with open('data/users.json', 'r') as json_file:
    json_data = json.load(json_file)
    json_data["users"].append(name)
with open('data/users.json', 'w') as json_file:
    json.dump(json_data, json_file)

edited Mar 15, 2018 at 19:48

answered Mar 14, 2018 at 22:00

Brendan Abel

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