How can I POST JSON data with Python's Requests library?

I need to POST JSON content 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 hard-coded JSON content from the server (the code is not shown), but when I try to POST JSON content 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())

How can I fix this problem?

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
200
>>> 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'}


Stack Overflow Q#9733638, score: 1808