Why can't Python parse this JSON data? [closed]

Question

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?

Gastrostomy

This question's status was discussed here. Community consensus was that this question was "good enough" to be left open after substantial edits. Please open a new discussion if you feel something has changed since that discussion. – Quadrillion

This question is being discussed on meta for a second time. – Doll

Answer 1

Your data is not valid JSON format. You have [] when you should have {} for the "masks" and "parameters" elements:

• [] 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.

Bogtrotter

serialized data is wrapped with [] , and when you read it in you need f.read(), that is if you use the standard. – Sporocyte

Thanks for the solution. i'm getting a unicode symbol while printing it. (eg u'valore' ). How to prevent it? – Sounding

Nice but python adds a u' before each key. Any idea why? – Repairer

That is why your text is type unicode not string. Most time it is better to have text in unicode for german umlauts and for sharing text results with other modules/programs etc. . So you're good! – Extortionate

How to know size of the maps array to control index in this example?data["maps"][0]["id"] - Here 0 hard coded. – Pacesetter

isn't there a resource leak because the handle to data.json is never closed? – Windham

In python 3, my json file is an array [] of jsons, it's called valid json by online checkers, and with these commands it loaded perfectly. Perhaps the definitions have changed circa 2018? – Erin

@nikhilvj json doesn't need to have {} at the root level. It can start with an array at the root level ([]) – Bogtrotter

https://mcmap.net/q/46156/-39-dict-39-object-has-no-attribute-39-read-39 need this piece for it to work. – Ellon

What exception will be thrown if the with call fails? Should this be wrapped in a try catch? – Ellon

@JustinPeel is there any chance that the order of the elements that are in the array (value of maps) will be changed. For example storing it into a data store (elastic search or any database) and then getting it back from there. – Schoolmarm

Answer 2

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'

Maladapted

Referring to 2.6 documentation (docs.python.org/2.6/library/io.html), opening a file in the "with" context will automatically close the file. – Earthen

@SteveS. Yes, but not before the context is left. pprinting in the with-context keeps the data_file open longer. – Maladapted

Is there a way to access like data.om_points or data.masks.id? – Nostradamus

This works except when I try to use a numbered index like data["maps"][0]["id"] I see error: KeyError: 0 – Nephoscope

@GayanPathirage you access it like data["om_points"] , data["masks"]["id"]. The idea is you can reach any level in a dictionary by specifying the 'key paths'. If you get a KeyError exception it means the key doesn't exist in the path. Look out for typos or check the structure of your dictionary. – Meliamelic

Answer 3

Here you go with modified data.json file:

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

You can call or print data on console by using below lines:

import json
from pprint import pprint
with open('data.json') as data_file:
    data_item = json.load(data_file)
pprint(data_item)

Expected output for print(data_item['parameters'][0]['id']):

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

Expected output for print(data_item['parameters'][0]['id']):

valore

Bigg

If we would like add a column to count how many observations does "maps" have, how could we write this function? – Alcides