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.

When you say it doesn't work, what exactly do you mean? From the last "Note" it sounds like it's more than just "ignores my data" (because _without_ the data "everything works fine"), but then exactly what _does_ happen? — abarnert, Dec 18 '12 at 21:36
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 ? — Suave Nti, Dec 18 '12 at 21:40
Have you tried `data = {"data": 24.3}` (note: a float, not a string)? I don't know WCF, but here's another interpretation: `string test(string data)` might mean that your server expects a single string as an input (`data_json = '"something"'` (note: it is a Python string that contains json text that represents json string)), and it doesn't expect a json object. Strictly speaking "application/json" must represent either a json object (e.g., `data_json = '{"a", 1}'`) or a json array (e.g., `data_json = '[1,2,3]'`) therefore it is incorrect to accept just a string. — jfs, Dec 18 '12 at 22:14

Martijn Pieters · Accepted Answer · 2014-12-07T02:39:14.873

28

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)

edited Dec 07 '14 at 02:39

answered Dec 18 '12 at 21:26

Martijn Pieters

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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 Dec 18 '12 at 21:31
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 ? – Suave Nti Dec 18 '12 at 21:37
2

@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 Dec 18 '12 at 21:54
@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. – Martijn Pieters Dec 18 '12 at 22:03
agreed with your comment server is expecting a json string so I need to pass a json string rather than an object. Thanks Cheers !! – Suave Nti Dec 18 '12 at 22:18
@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. – abarnert Dec 18 '12 at 22:30

REST post using Python-Request

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