This is how you do it.

from urllib import request, parse
data = parse.urlencode(<your data dict>).encode()
req =  request.Request(<your url>, data=data) # this will make the method "POST"
resp = request.urlopen(req)

This may have been answered before: Python URLLib / URLLib2 POST.

Your server is likely performing a 302 redirect from http://myserver/post_service to http://myserver/post_service/. When the 302 redirect is performed, the request changes from POST to GET (see Issue 1401). Try changing url to http://myserver/post_service/.

HTTP POST works as expected:

#!/usr/bin/env python
from contextlib import closing
try:
    from urllib.parse import urlencode
    from urllib.request import urlopen
except ImportError: # Python 2
    from urllib import urlencode
    from urllib2 import urlopen

url = 'http://httpbin.org/post'
data = urlencode({"field1" : "value", "Submit": "Save"}).encode()
with closing(urlopen(url, data)) as response:
    print(response.read().decode())

You may see GET only after an http redirect (as the rfc recommends -- no data should be posted on redirect without prompting the user).

For example, here's an http server that redirects POST / requests:

#!/usr/bin/env python
from flask import Flask, redirect, request, url_for # $ pip install flask

app = Flask(__name__)

@app.route('/', methods=['GET', 'POST'])
def index():
    if request.method == 'POST':
        return redirect(url_for('post'))
    return '<form method="POST"><input type="submit">'


@app.route('/post', methods=['GET', 'POST'])
def post():
    return 'Hello redirected %s!' % request.method

if __name__ == '__main__':
    import sys
    port = int(sys.argv[1]) if len(sys.argv) > 1 else None
    app.run(host='localhost', port=port)

Making an HTTP POST request using the same code (urlopen(url, data)) leads to the redirection and the second request is GET:

"POST / HTTP/1.1" 302 -
"GET /post HTTP/1.1" 200 -

Again, the first request is POST, not GET. The behavior is exactly the same if you visit / and click submit button (the browser makes POST request and then GET request).

Python issue: "Document how to forward POST data on redirects" contains a link to HTTPRedirectHandler's subclass that posts data on redirect:

#!/usr/bin/env python
from contextlib import closing
try:
    from urllib.parse import urlencode
    from urllib.request import (HTTPError, HTTPRedirectHandler, Request,
                                build_opener, urlopen)
except ImportError: # Python 2
    from urllib import urlencode
    from urllib2 import (HTTPError, HTTPRedirectHandler, Request,
                         build_opener, urlopen)

class PostHTTPRedirectHandler(HTTPRedirectHandler):
    """Post data on redirect unlike urrlib2.HTTPRedirectHandler."""
    def redirect_request(self, req, fp, code, msg, headers, newurl):
        m = req.get_method()
        if (code in (301, 302, 303, 307) and m in ("GET", "HEAD")
            or code in (301, 302, 303) and m == "POST"):
            newurl = newurl.replace(' ', '%20')
            CONTENT_HEADERS = ("content-length", "content-type")
            newheaders = dict((k, v) for k, v in req.headers.items()
                              if k.lower() not in CONTENT_HEADERS)
            return Request(newurl,
                           data=req.data,
                           headers=newheaders,
                           origin_req_host=req.origin_req_host,
                           unverifiable=True)
        else:
            raise HTTPError(req.get_full_url(), code, msg, headers, fp)


urlopen = build_opener(PostHTTPRedirectHandler).open

url = 'http://localhost:5000'
data = urlencode({"field1" : "value", "Submit": "Save"}).encode()
with closing(urlopen(url, data)) as response:
    print(response.read().decode())

The access log shows two POST requests in this case (the second request is POST):

"POST / HTTP/1.1" 302 -
"POST /post HTTP/1.1" 200 -

Note: you could customize the HTTPRedirectHandler to follow the rfc 2616 behavior.

This would be the equivalent request using the python requests library.

url = "https://api.infermedica.com/dev/parse"
headers = {
    'App_Id': '4c177c',
    'App_Key': '6852599182ba85d70066986ca2b3',
    'Content-Type': 'application/json',
}
data = {'text': 'i feel stomach pain but no coughing today'}

r = requests.post(url, headers=headers, data=json.dumps(data))
print r.status_code
print r.json()

But your real problem is that you're using the wrong header keys for their api. It's App-Id and App-key, not App_Id and App_key. It would look like this:

headers = {
    'App-Id': 'xx', 
    'App-key': 'xxxx', 
    'Accept': 'application/json', 
    'Content-Type': 'application/json',
    'Dev-Mode': 'true'}

data = {'text': 'i feel stomach pain but no coughing today'}
r = requests.post(url, headers=headers, data=json.dumps(data))

Also worth noting, they have a python api that does all this for you.

u = urllib2.urlopen('http://myserver/inout-tracker', data)
h.request('POST', '/inout-tracker/index.php', data, headers)

Using the path /inout-tracker without a trailing / doesn't fetch index.php. Instead the server will issue a 302 redirect to the version with the trailing /.

Doing a 302 will typically cause clients to convert a POST to a GET request.

details = urllib.parse.urlencode({'IDToken1': 'USERNAME', 'IDToken2': 'PASSWORD'})

Add the following line:

details = details.encode('UTF-8')