Error, Retrieving a web page with data in Python 3

I have written a very basic Python 3 function to retrieve a web page with some data but I am getting an error message:

import urllib.parse
开发者_JS百科import urllib.request

def fetch_web (url, par1,par2="",par3=""):

    values  = {"s":"stor","l":"SVEENG"}
    data = urllib.parse.urlencode(values)
    req = urllib.request.Request(url,data)

    response = urllib.request.urlopen(req)

    page = response.read()

url = "http://wwww.ord.se"
fetch_web(url,"stor")

When executing this program I am getting following error message:

TypeError: POST data should be bytes or an iterable of bytes. It cannot be str.

Any ideas about the misstake?

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You should learn about Bytes vs Characters in Python 3.

And them use byte strings like: b'...' for data you post to a website.