HTTPS POST request Python, returning .csv

I want to make a post request to a HTTPS-site that should respond with a .csv file. I have this Python code:

try:
    #conn = httplib.HTTPSConnection(host="www.site.com", port=443)

=> Gives an BadStatusLine: ' ' error

    conn = httplib.HTTPConnection("www.site.com");
    params  = urllib.urlencode({'val1':'123','val2':'abc','val3':'1b3'})
    conn.request("POST", "/nps/servlet/exportdatadownload", params)
    content = conn.getresponse()
    print content.reason, content.status
    print content.read()
    conn.close()
except:
    import sys
    print sys.exc_info()[:2]

Output:

Found 302

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<HTML><HEAD>
<TITLE>302 Found</TITLE>
</HEAD><BODY>
<H1>Found</H1>
The document has moved <A HREF="https://www.site.com/nps/servlet/exportdatadownload">here</A>.<P>
<HR>
<ADDRESS>Oracle-Application-Server-10g/10.1.3.5.0 Oracle-HTTP-Server Server at mp-www1.mrco.be Port 7778</ADDRESS>
</BODY></HTML>

What am I doing wrong? How do I 'catch' the returning .csv file? I tried the POST request with an Chrome Extentions (Advanced Rest Client, and that's working...)

The HTML output with the 302 error is because you're connecting to the site using HTTP instead of HTTPS, which is in your code here:

conn = httplib.HTTPConnection("www.site.com");

Presumably you're doing that because of some other error with the commented out section of your code.

If I were trying to do this I would use Requests, which comes with very clear documentation. With Requests the code would be something like:

import requests

url = "https://www.example.com/nps/servlet/exportdatadownload"
payload = { "val1": "123", "val2": "abc", "val3": "1b3" }
r = requests.post(url, data=payload, verify=True)

The CSV file should be in r.content, which can be written to a file.