Accessing a single dictionary in a list inside a json file

Question

I have JSON file with the structure like this. This JSON file is the annotation data from my dataset, and I want to used for my YOLO object detection.

{
    "description": "",
    "tags": [],
    "size": {
        "height": 720,
        "width": 1280
    },
    "objects": [
        {
            "id": 768275656,
            "classId": 3753641,
            "description": "",
            "geometryType": "rectangle",
            "labelerLogin": "monochloride",
            "createdAt": "2021-07-20T00:50:24.512Z",
            "updatedAt": "2021-07-20T00:50:24.512Z",
            "tags": [],
            "classTitle": "II",
            "points": {
                "exterior": [
                    [
                        383,
                        230
                    ],
                    [
                        659,
                        417
                    ]
                ],
                "interior": []
            }
        }
    ]
}

What I want to do is parsing the information from "exterior" in "objects" field, which contains the information of bounding box but I haven't succeeded in doing it.

Previously I tried to access the value using this code

x1 = data['objects'][0]['points']['exterior'][0][0]
y1 = data['objects'][0]['points']['exterior'][0][1]
x2 = data['objects'][0]['points']['exterior'][1][0]
y2 = data['objects'][0]['points']['exterior'][1][1]

but the program throws

IndexError: list index out of range .

Where did I do it wrong, and how to solve it?

Answer 1

It seems that you were missing a opening curly brace, the following based on your code works just fine:

import json

# open json file
with open('yoloobject.json', 'r') as f:
    jsonstring = f.read()
    f.seek(0,0)
    data = json.load(f)


print('Json String: ', jsonstring)

x1 = data['objects'][0]['points']['exterior'][0][0]
y1 = data['objects'][0]['points']['exterior'][0][1]
x2 = data['objects'][0]['points']['exterior'][1][0]
y2 = data['objects'][0]['points']['exterior'][1][1]

print(f'bounding box: ({x1},{y2}), ({x2},{y2})')

with outputs:

Json String:  {
    "description": "",
    "tags": [],
    "size": {
        "height": 720,
        "width": 1280
    },
    "objects": [{
            "id": 768275656,
            "classId": 3753641,
            "description": "",
            "geometryType": "rectangle",
            "labelerLogin": "monochloride",
            "createdAt": "2021-07-20T00:50:24.512Z",
            "updatedAt": "2021-07-20T00:50:24.512Z",
            "tags": [],
            "classTitle": "II",
            "points": {
                "exterior": [
                    [
                        383,
                        230
                    ],
                    [
                        659,
                        417
                    ]
                ],
                "interior": []
            }
        }
    ]
}
bounding box: (383,417), (659,417)