How to dynamically build a JSON object with Python?

How to dynamically build a JSON object with Python?

  1. Question by Backo
  2. Answer by Martijn Pieters♦
  3. Answer by Milovan Tomašević
    1. from string
    2. from file:
    3. from requests

Question by Backo

I am new to Python and I am playing with JSON data. I would like to dynamically build a JSON object by adding some key-value to an existing JSON object.

I tried the following but I get TypeError: 'str' object does not support item assignment:

import json

json_data = json.dumps({})
json_data["key"] = "value"

print 'JSON: ', json_data

Answer by Martijn Pieters♦

You build the object before encoding it to a JSON string:

import json

data = {}
data['key'] = 'value'
json_data = json.dumps(data)

JSON is a serialization format, textual data representing a structure. It is not, itself, that structure.

Answer by Milovan Tomašević

  • json.loads take a string as input and returns a dictionary as output.
  • json.dumps take a dictionary as input and returns a string as output.

If you need to convert JSON data into a python object, it can do so with Python3, in one line without additional installations, using SimpleNamespace and object_hook:

from string

import json
from types import SimpleNamespace

string = '{"foo":3, "bar":{"x":1, "y":2}}'

# Parse JSON into an object with attributes corresponding to dict keys.
x = json.loads(string, object_hook=lambda d: SimpleNamespace(**d))

print(x.foo)
print(x.bar.x)
print(x.bar.y)

output:

3
1
2

from file:

JSON object: data.json

{
    "foo": 3,
    "bar": {
        "x": 1,
        "y": 2
    }
}
import json
from types import SimpleNamespace

with open("data.json") as fh:
    string = fh.read()

# Parse JSON into an object with attributes corresponding to dict keys.
x = json.loads(string, object_hook=lambda d: SimpleNamespace(**d))

print(x.foo)
print(x.bar.x)
print(x.bar.y)

output:

3
1
2

from requests

import json
from types import SimpleNamespace
import requests

r = requests.get('https://api.github.com/users/MilovanTomasevic')

# Parse JSON into an object with attributes corresponding to dict keys.
x = json.loads(r.text, object_hook=lambda d: SimpleNamespace(**d))

print(x.name)
print(x.company)
print(x.blog)

output:

Milovan Tomašević
NLB
milovantomasevic.com

For more beautiful and faster access to JSON response from API, take a look at this response.


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