REST post using Python-Request

Question

Why doesn't this simple code POST data to my service:

import requests
import json

data = {"data" : "24.3"}
data_json = json.dumps(data)
response = requests.post(url, data=data_json)
print response.text

And my service is developed using WCF like this :

  [OperationContract]
  [WebInvoke(Method = "POST", UriTemplate = "/test", ResponseFormat =    
      WebMessageFormat.Json,RequestFormat=WebMessageFormat.Json)]
  string test(string data );

Note: If is remove the input parameter data everything works fine, what may be the issue.

Solution

You need to set the content type header:

data = {"data" : "24.3"}
data_json = json.dumps(data)
headers = {'Content-type': 'application/json'}

response = requests.post(url, data=data_json, headers=headers)

If I set url to http://httpbin.org/post, that server echos back to me what was posted:

>>> import json
>>> import requests
>>> import pprint
>>> url = 'http://httpbin.org/post'
>>> data = {"data" : "24.3"}
>>> data_json = json.dumps(data)
>>> headers = {'Content-type': 'application/json'}
>>> response = requests.post(url, data=data_json, headers=headers)
>>> pprint.pprint(response.json())
{u'args': {},
 u'data': u'{"data": "24.3"}',
 u'files': {},
 u'form': {},
 u'headers': {u'Accept': u'*/*',
              u'Accept-Encoding': u'gzip, deflate, compress',
              u'Connection': u'keep-alive',
              u'Content-Length': u'16',
              u'Content-Type': u'application/json',
              u'Host': u'httpbin.org',
              u'User-Agent': u'python-requests/1.0.3 CPython/2.6.8 Darwin/11.4.2'},
 u'json': {u'data': u'24.3'},
 u'origin': u'109.247.40.35',
 u'url': u'http://httpbin.org/post'}
>>> pprint.pprint(response.json()['json'])
{u'data': u'24.3'}

If you are using requests version 2.4.2 or newer, you can leave the JSON encoding to the library; it'll automatically set the correct Content-Type header for you too. Pass in the data to be sent as JSON into the json keyword argument:

data = {"data" : "24.3"}
response = requests.post(url, json=data)

Comments

[Suave Nti]

Tried with Content-type earlier but no luck. Is there any problem with my WCF .. If I remove the Input param I can call the URL. I dunno what may be the issue.

[Suave Nti]

Well I think I found the issue. It is with the {"data" : "24.3"} .. for some reasons I need to enclose that as a string thats when my request is going through.. like this "{data : 24.3}" .. anyone care to explain reasons ?

[Martijn Pieters]

@GJSJ: then you are no longer sending a JSON object, but a JSON string. That'd be a server-side issue, nothing to do with Python or requests.

[Martijn Pieters]

@GJSJ: just try that out with http://httpbin.org/post as the URL; it responds with a JSON structure, including a json key to show you what JSON it received if you send JSON.

[Suave Nti]

agreed with your comment server is expecting a json string so I need to pass a json string rather than an object. Thanks Cheers !!

[abarnert]

@GJSJ: Often this means whoever coded the server put a json.loads/JSON.decode/equivalent in the script, even though the server container or framework has already done the decoding, so the service only works if the client "double-encodes" the data. (Which, as J.F. Sebastian points out, is actually not legal for application/json, but most servers won't care.) The right fix is to fix the server… but if it's not something you have control over, your workaround is basically equivalent to double-encoding, so it works just as well.