Python 3 urllib produces TypeError: POST data should be bytes or an iterable of bytes. It cannot be of type str

From the docs Note that params output from urlencode is encoded to bytes before it is sent to urlopen as data:

data = urllib.parse.urlencode(d).encode("utf-8")
req = urllib.request.Request(url)
with urllib.request.urlopen(req,data=data) as f:
    resp = f.read()
    print(resp)