Why can”t Python parse this JSON data?

StackOverflow

I have this JSON in a file:

{
    "maps": [
        {
            "id": "blabla",
            "iscategorical": "0"
        },
        {
            "id": "blabla",
            "iscategorical": "0"
        }
    ],
    "masks": [
        "id": "valore"
    ],
    "om_points": "value",
    "parameters": [
        "id": "valore"
    ]
}

I wrote this script to print all of the JSON data:

import json
from pprint import pprint

with open("data.json") as f:
    data = json.load(f)

pprint(data)

This program raises an exception, though:

Traceback (most recent call last):
  File "<pyshell#1>", line 5, in <module>
    data = json.load(f)
  File "/usr/lib/python3.5/json/__init__.py", line 319, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.5/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.5/json/decoder.py", line 355, in raw_decode
    obj, end = self.scan_once(s, idx)
json.decoder.JSONDecodeError: Expecting "," delimiter: line 13 column 13 (char 213)

How can I parse the JSON and extract its values?

Answer rating: 2180

Your data is not valid JSON format. You have [] when you should have {}:

  • [] are for JSON arrays, which are called list in Python
  • {} are for JSON objects, which are called dict in Python

Here"s how your JSON file should look:

{
    "maps": [
        {
            "id": "blabla",
            "iscategorical": "0"
        },
        {
            "id": "blabla",
            "iscategorical": "0"
        }
    ],
    "masks": {
        "id": "valore"
    },
    "om_points": "value",
    "parameters": {
        "id": "valore"
    }
}

Then you can use your code:

import json
from pprint import pprint

with open("data.json") as f:
    data = json.load(f)

pprint(data)

With data, you can now also find values like so:

data["maps"][0]["id"]
data["masks"]["id"]
data["om_points"]

Try those out and see if it starts to make sense.

Answer rating: 320

Your data.json should look like this:

{
 "maps":[
         {"id":"blabla";"iscategorical":"0"},
         {"id":"blabla";"iscategorical":"0"}
        ],
"masks":
         {"id":"valore"},
"om_points":"value",
"parameters":
         {"id":"valore"}
}

Your code should be:

import json
from pprint import pprint

with open("data.json") as data_file:    
    data = json.load(data_file)
pprint(data)

Note that this only works in Python 2.6 and up, as it depends upon the with-statement. In Python 2.5 use from __future__ import with_statement, in Python <= 2.4, see Justin Peel"s answer, which this answer is based upon.

You can now also access single values like this:

data["maps"][0]["id"]  # will return "blabla"
data["masks"]["id"]    # will return "valore"
data["om_points"]      # will return "value"

Answer rating: 75

Justin Peel"s answer is really helpful, but if you are using Python 3 reading JSON should be done like this:

with open("data.json", encoding="utf-8") as data_file:
    data = json.loads(data_file.read())

Note: use json.loads instead of json.load. In Python 3, json.loads takes a string parameter. json.load takes a file-like object parameter. data_file.read() returns a string object.

To be honest, I don"t think it"s a problem to load all json data into memory in most cases. I see this in JS, Java, Kotlin, cpp, rust almost every language I use. Consider memory issue like a joke to me :)

On the other hand, I don"t think you can parse json without reading all of it.





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