Trouble with reading json files in python

Question

I have a json file that looks like this:

[
 {
 "image_path": "train640x480/2d4_2.bmp",
 "rects": [
 {
 "y2": 152.9,
 "y1": 21.2,
 "x2": 567.3,
 "x1": 410.8
 }
 ]
 },
 {
 "image_path": "train640x480/1dd_1.bmp",
 "rects": [
 {
 "y2": 175.1,
 "y1": 74.7,
 "x2": 483.8,
 "x1": 230.8
 }
 ]
 }
]

When I do

H = {}
with open('train.json', 'r') as json_data:
 H = json.load(json_data)
 print(H)

It prints out this

How do I access the rectangle values of each image? I've tried

H['image_path:'][os.path.join(directory, filename)]

but that returns

TypeError: list indices must be integers or slices, not str

Any help would be appreciated.

Answer 1

Your json file contains a list of dictionaries, which means that you first need to loop through the list, before accessing the contents of the dictionaries.

e.g.

for items in H:
 if items['image_path'] == os.path.join(directory, filename):
 print items['rects']

If your json had looked like this, you would be able to access the entries like you are expecting.

{
 "train640x480/2d4_2.bmp":
 {
 "rects": [
 {
 "y2": 152.9,
 "y1": 21.2,
 "x2": 567.3,
 "x1": 410.8
 }
 ]
 },
 "train640x480/1dd_1.bmp":
 {
 "rects": [
 {
 "y2": 175.1,
 "y1": 74.7,
 "x2": 483.8,
 "x1": 230.8
 }
 ]
 }
}

e.g.

print H['train640x480/2d4_2.bmp']['rects]

• Kevin Qiu: Thank you very much! I did wonder why my json file started and ended with a [ and ] instead of {}

Answer 2

You should first put a number as a index to access the first list. Your json data is structured as a list then dictionary then list then dictionary of the vertices. Your query should be

H[0]["rects"][0] # the fist rectangle dictionary

And

H[1]["rects"][0] # the second rectangle dictionary

Answer 3

Try this code

print H[0]["image_path"]
print H[0]["rects"][0]["y2"]
print H[1]["image_path"]
print H[1]["rects"][0]["y2"]