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I need to POST a JSON from a client to a server. I'm using Python 2.7.1 and simplejson. The client is using Requests. The server is CherryPy. I can GET a hard-coded JSON from the server (code not shown), but when I try to POST a JSON to the server, I get "400 Bad Request".

Here is my client code:

data = {'sender':   'Alice',
    'receiver': 'Bob',
    'message':  'We did it!'}
data_json = simplejson.dumps(data)
payload = {'json_payload': data_json}
r = requests.post("http://localhost:8080", data=payload)

Here is the server code.

class Root(object):
    def __init__(self, content):
        self.content = content
        print self.content  # this works
    exposed = True
    def GET(self):
        cherrypy.response.headers['Content-Type'] = 'application/json'
        return simplejson.dumps(self.content)
    def POST(self):
        self.content = simplejson.loads(cherrypy.request.body.read())

Any ideas?

My comment still stands - CherryPy does not call class __init__ methods with a content argument (and does not claim to in the link you supply). In the detailed example they have, the user supplies the code that calls __init__ and provides the arguments, which we have not seen here so I have no idea what state your object is in when your # this works comment is relevant. – Nick Bastin Mar 31, 2012 at 2:49 yeah, I was trying to start up your example in order to test it, and I wasn't sure how you were instantiating it. – Nick Bastin Mar 31, 2012 at 4:02 Alternatively, If you use a tool like Postman to test your API calls, you can generate code snippet. Like snippets in Python that uses the requests package. Postman documentation – amiabl Jun 7, 2019 at 12:56

Starting with Requests version 2.4.2, you can use the json= parameter (which takes a dictionary) instead of data= (which takes a string) in the call:

>>> import requests
>>> r = requests.post('http://httpbin.org/post', json={"key": "value"})
>>> r.status_code
>>> r.json()
{'args': {},
 'data': '{"key": "value"}',
 'files': {},
 'form': {},
 'headers': {'Accept': '*/*',
             'Accept-Encoding': 'gzip, deflate',
             'Connection': 'close',
             'Content-Length': '16',
             'Content-Type': 'application/json',
             'Host': 'httpbin.org',
             'User-Agent': 'python-requests/2.4.3 CPython/3.4.0',
             'X-Request-Id': 'xx-xx-xx'},
 'json': {'key': 'value'},
 'origin': 'x.x.x.x',
 'url': 'http://httpbin.org/post'}
                Setting this to the accepted answer since this is more idiomatic as of 2.4.2. Keep in mind, for crazy unicode, this may not work.
– Charles R
                Sep 23, 2015 at 23:00
                I saw an example of this that took the dict object and performed json.dumps(object) before sending. Don't do this...it messes up your JSON. The above is perfect..you can pass it a python object and it turns into perfect json.
– MydKnight
                May 15, 2020 at 23:13
                @MydKnight looking at the source code, Requests sets the content type then does json.dumps(your_json) and converts the result from a str to bytes.
– Boris Verkhovskiy
                Jan 12, 2021 at 18:18
                I logged into my account especially to give you +1 for this. Thanks. I was stuck for a couple of hours until I saw you could specify json=dict  It' a script for Linode DNS API that I am working on. Thank you very much!
– bitofagoob
                Jan 30, 2022 at 23:27
                Before I found this answer I had also to use data=json.dumps(...) but without Content-type: application/json in the header it wouldn't work. This json=... thing works perfect.
– elano7
                Jul 1, 2022 at 8:30
url = "http://localhost:8080"
data = {'sender': 'Alice', 'receiver': 'Bob', 'message': 'We did it!'}
headers = {'Content-type': 'application/json', 'Accept': 'text/plain'}
r = requests.post(url, data=json.dumps(data), headers=headers)
                Good catch - I saw your application/json in GET and somehow missed that you hadn't provided it on the request.  You may also need to make sure that you return something from POST or you might get a 500.
– Nick Bastin
                Mar 31, 2012 at 4:01
                Little heads up before using json.dumps here. The data parameter of requests works fine with dictionaries. No need for converting to a string.
– Advait Saravade
                Jul 2, 2018 at 6:32

From requests 2.4.2 (https://pypi.python.org/pypi/requests), the "json" parameter is supported. No need to specify "Content-Type". So the shorter version:

requests.post('http://httpbin.org/post', json={'test': 'cheers'})

Which parameter between data / json / files you need to use depends on a request header named Content-Type (you can check this through the developer tools of your browser).

When the Content-Type is application/x-www-form-urlencoded, use data=:

requests.post(url, data=json_obj)

When the Content-Type is application/json, you can either just use json= or use data= and set the Content-Type yourself:

requests.post(url, json=json_obj)
requests.post(url, data=jsonstr, headers={"Content-Type":"application/json"})

When the Content-Type is multipart/form-data, it's used to upload files, so use files=:

requests.post(url, files=xxxx)
                +1. If you're using curlify to see the request made from the response, the content type header will not be set unless you follow these instructions.  print(curlify.to_curl(project.request))
– Olshansky
                Apr 12, 2021 at 20:54
                The key realization is that every parameter will perform automagic serialization without regard for the current value of the Content-Type header. Consequently, data=json_obj is basically always incorrect; the value must be stringified first, either explicitly by the caller or implicitly via the json parameter.
– mkjeldsen
                Apr 22, 2022 at 7:43
headers = {"charset": "utf-8", "Content-Type": "application/json"}
url = 'http://localhost:PORT_NUM/FILE.php'
r = requests.post(url, json=YOUR_JSON_DATA, headers=headers)
print(r.text)
    'receiver': 'Bob',
    'message':  'We did it!'}
r = requests.post("http://localhost:8080", json={'json_payload': data})

server:

class Root(object):
    def __init__(self, content):
        self.content = content
        print self.content  # this works
    exposed = True
    def GET(self):
        cherrypy.response.headers['Content-Type'] = 'application/json'
        return simplejson.dumps(self.content)
    @cherrypy.tools.json_in()
    @cherrypy.tools.json_out()
    def POST(self):
        self.content = cherrypy.request.json
        return {'status': 'success', 'message': 'updated'}
                Note/reminder: the json arg automatically adds the content-type header for POST in newer versions of Python.
– MarkHu
                Feb 15, 2022 at 19:59

With current requests you can pass in any data structure that dumps to valid JSON , with the json parameter, not just dictionaries (as falsely claimed by the answer by Zeyang Lin).

import requests
r = requests.post('http://httpbin.org/post', json=[1, 2, {"a": 3}])

this is particularly useful if you need to order elements in the response.

I solved it this way:

from flask import Flask, request
from flask_restful import Resource, Api
req = request.json
if not req :
    req = request.form
req['value']

It always recommended that we need to have the ability to read the JSON file and parse an object as a request body. We are not going to parse the raw data in the request so the following method will help you to resolve it.

def POST_request():
    with open("FILE PATH", "r") as data:
        JSON_Body = data.read()
    response = requests.post(url="URL", data=JSON_Body)
    assert response.status_code == 200