Python: How to append a JSON object to a JSON array

Question

I would like to append a JSON object that contains example informations to "list" JSON array from my python file to my JSON file

My python file:

import json

with open("mydata.json", "r+") as f:
    data = json.load(f)
    data["list"].append(
        {"a": "1"}
    )

    json.dump(data, f, indent=4)

My JSON file:

{
    "list": [

    ]
}

I was expecting this result from my JSON file:

{
    "list": [
        {
            "a": "1"
        }
    ]
}

But I got this instead:

{
    "list": [

    ]
}{
    "list": [
        {
            "a": "1"
        }
    ]
}

Do you guys have any idea why this happended and how to fix it?

Answer 1

You dumped the updated JSON at the end of the original file, rather than replacing it. You should reopen the file to overwrite it.

import json

with open("mydata.json", "r") as f:
    data = json.load(f)
data["list"].append(
    {"a": "1"}
)
with open("mydata.json", "w") as f:
    json.dump(data, f, indent=4)