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Python3: JSON POST Request WITHOUT requests library

I want to send JSON encoded data to a server using only native Python libraries. I love requests but I simply can’t use it because I can’t use it on the machine which runs the script. I need to do it without.

newConditions = {"con1":40, "con2":20, "con3":99, "con4":40, "password":"1234"} 
params = urllib.parse.urlencode(newConditions)
params = params.encode('utf-8')

req = urllib.request.Request(conditionsSetURL, data=params)
urllib.request.urlopen(req)

My server is a local WAMP server. I always get an

urllib.error.HTTPError: HTTP Error 500: Internal Server Error

I am 100% sure that this is NOT a server issue, because the same data, with the same url, on the same machine, with the same server works with the requests library and Postman.

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Answer

You are not posting JSON, you are posting a application/x-www-form-urlencoded request.

Encode to JSON and set the right headers:

import json

newConditions = {"con1":40, "con2":20, "con3":99, "con4":40, "password":"1234"} 
params = json.dumps(newConditions).encode('utf8')
req = urllib.request.Request(conditionsSetURL, data=params,
                             headers={'content-type': 'application/json'})
response = urllib.request.urlopen(req)

Demo:

>>> import json
>>> import urllib.request
>>> conditionsSetURL = 'http://httpbin.org/post'
>>> newConditions = {"con1":40, "con2":20, "con3":99, "con4":40, "password":"1234"} 
>>> params = json.dumps(newConditions).encode('utf8')
>>> req = urllib.request.Request(conditionsSetURL, data=params,
...                              headers={'content-type': 'application/json'})
>>> response = urllib.request.urlopen(req)
>>> print(response.read().decode('utf8'))
{
  "args": {}, 
  "data": "{"con4": 40, "con2": 20, "con1": 40, "password": "1234", "con3": 99}", 
  "files": {}, 
  "form": {}, 
  "headers": {
    "Accept-Encoding": "identity", 
    "Connection": "close", 
    "Content-Length": "68", 
    "Content-Type": "application/json", 
    "Host": "httpbin.org", 
    "User-Agent": "Python-urllib/3.4", 
    "X-Request-Id": "411fbb7c-1aa0-457e-95f9-1af15b77c2d8"
  }, 
  "json": {
    "con1": 40, 
    "con2": 20, 
    "con3": 99, 
    "con4": 40, 
    "password": "1234"
  }, 
  "origin": "84.92.98.170", 
  "url": "http://httpbin.org/post"
}
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