Python Flask-Restful POST not taking JSON arguments

Question

I am very new to Flask (& Flask-Restful).

My problem : json arguments for a POST is getting set to NONE (not working).

I am able to take arguments from the form-data, using POSTMAN plugin for chrome. But, when i switch to raw (& feed a json), it fails to read the json & assigns a NONE to all my arguments.

I have read some related stackoverflow posts related to this : link1, link2, link3 ... none of these helped me.

I am using python-2.6, Flask-Restful-0.3.3, Flask-0.10.1, Chrome, POSTMAN on Oracle Linux 6.5.

Python code app.py :

from flask import Flask, jsonify
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):
        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)

Testing this using POSTMAN :

Using form-data : works perfectly !
Using raw -> json : causes this issue

Things tried #1 :

Add json parameter to my add_argument() method in app.py

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

Input : { "username": "hello", "password": "world" }

Output : { "p": "None", "u": "None" }

Things tried #2 :

Change type to unicode in add_argument() method in app.py

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

Input : { "username": "hello", "password": "world" }

Output : { "p": "None", "u": "None" }

PS : I will keep updating my question, with every failed attempt. Please let me know if you need any more info to make this question more clear.

Looks to me like you're missing a call to `parser.parse_args()`. You should have `args = parser.parse_args()` before you can access the `args` — junnytony, May 27 '15 at 20:12
@junnytony - its a typo from my side, i forgot to copy that line. Editing the question right away! — sudhishkr, May 27 '15 at 20:14

score 36 · Answer 1 · answered May 27 '15 at 21:32

36

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)

answered May 27 '15 at 21:32

sudhishkr

3,318
5
33
55

Nice :). but I think your code would be even more awesome if you changed the mimetype for your post to be 'application/json'. I'm guessing you're using AJAX for your post. With something like jQuery you can easily add the appropriate mimetype for example http://stackoverflow.com/questions/6323338/jquery-ajax-posting-json-to-webservice – junnytony May 27 '15 at 22:28
1

Thanks for providing your final code, I have a similar use case. – Brian Wylie Jul 17 '15 at 15:21
HI, I am also facing the same issue.As per your suggestion I done but still getting bad request error – KCN Jun 13 '17 at 07:57
what your exact issue @KCN? – sudhishkr Jun 13 '17 at 18:41
1

As per your suggestion I followed like json_dat = request.get_json(force=True) fname = json_dat["firstname"] lname = json_dat["lastname"] but while executing this url from rest client getting 400 bad request error – KCN Jun 14 '17 at 04:40

score 29 · Accepted Answer · edited Jul 01 '16 at 12:46

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

Cleb · Answer 3 · 2019-01-26T20:52:50.677

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.

score 6 · Answer 4 · answered May 22 '19 at 22:51

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)

Python Flask-Restful POST not taking JSON arguments

4 Answers4

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