Python Flask-Restful POST not taking JSON arguments

junnytony's answer gave me a hint, and I went ahead with this approach. get_json seems to have done the trick.

from flask import Flask, jsonify, request
from flask_restful import reqparse, abort, Api, Resource

app = Flask(__name__)
api = Api(app)

#parser = reqparse.RequestParser()
#parser.add_argument('username', type=unicode, location='json')
#parser.add_argument('password', type=unicode, location='json')

class HelloWorld(Resource):
    def post(self):
        json_data = request.get_json(force=True)
        un = json_data['username']
        pw = json_data['password']
        #args = parser.parse_args()
        #un = str(args['username'])
        #pw = str(args['password'])
        return jsonify(u=un, p=pw)

api.add_resource(HelloWorld, '/testing')

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5444 ,debug=True)

I ran into a similar issue and here is a solution that works for me. let's say your application looks like this:

from flask import Flask, jsonify
from flask_restful import Api, Resource, reqparse

app = Flask(__name__)
api = Api(app)

# Define parser and request args
parser = reqparse.RequestParser()
parser.add_argument('last_name', type=str)
parser.add_argument('first_name', type=str)
# not the type=dict
parser.add_argument('personal_data', type=dict)


class Item(Resource):

    def post(self):

        args = parser.parse_args()

        ln = args['last_name']
        fn = args['first_name']
        # we can also easily parse nested structures
        age = args['personal_data']['age']
        nn = args['personal_data']['nicknames']

        return jsonify(fn=fn, ln=ln, age=age, nn=nn)


api.add_resource(Item, '/item')

if __name__ == '__main__':
    app.run(debug=True)

Now, you can easily create some JSON data:

import json

d = {'last_name': 'smith', 'first_name': 'john', 'personal_data': {'age': 18, 'height': 180, 'nicknames': ['johnny', 'grandmaster']}}

print(json.dumps(d, indent=4))

{
    "last_name": "smith",
    "first_name": "john",
    "personal_data": {
        "age": 18,
        "height": 180,
        "nicknames": [
            "johnny",
            "grandmaster"
        ]
    }
}

json.dumps(d)
'{"last_name": "smith", "first_name": "john", "personal_data": {"age": 18, "height": 180, "nicknames": ["johnny", "grandmaster"]}}'

and call the application:

curl http://localhost:5000/item -d '{"last_name": "smith", "first_name": "john", "personal_data": {"age": 18, "height": 180, "nicknames": ["johnny", "grandmaster"]}}'

This will crash with the error (I shortened the traceback):

age = args['personal_data']['age']
TypeError: 'NoneType' object is not subscriptable

the reason is that the header is not specified. If we add the

-H "Content-Type: application/json"

and then call

curl http://localhost:5000/item -H "Content-Type: application/json" -d '{"last_name": "smith", "first_name": "john", "personal_data": {"age": 18, "height": 180, "nicknames": ["johnny", "grandmaster"]}}'

The output looks as expected:

{
  "age": 18, 
  "fn": "john", 
  "ln": "smith", 
  "nn": [
    "johnny", 
    "grandmaster"
  ]
}

The function can be also further simplified to:

class Item(Resource):

    def post(self):

        json_data = request.get_json()
        # create your response below

as shown above.

According to the documentation for Request.json and the new Request.get_json, you should have the mimetype on your POST request set to application/json. This is the only way flask will automatically parse your JSON data into the Request.json property which (I believe) is what Flask-Restful depends on to retrieve JSON data.

NOTE: The newer get_json function has an option to force the parsing of POST data as JSON irrespective of the mimetype

After forcing the request to parse json, it worked with me. Here is the code:

from flask import Flask, jsonify, request
from flask_restful import reqparse, abort, Api, Resource

app = Flask(__name__)
api = Api(app)

parser = reqparse.RequestParser()
parser.add_argument('username', type=str)
parser.add_argument('password', type=str)

class HelloWorld(Resource):
    def post(self):
        request.get_json(force=True)
        args = parser.parse_args()
        un = str(args['username'])
        pw = str(args['password'])
        return jsonify(u=un, p=pw)

api.add_resource(HelloWorld, '/testing')

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5444 ,debug=True)