urllib.error.URLError: <urlopen error unknown url type: 'https>
You should use urllib.parse.urlencode(), urllib.parse.urljoin(), etc functions to construct urls instead of manually joining the strings. It would take care of : -> %3A conversion e.g.:
>>> import urllib.parse
>>> urllib.parse.quote(':')
'%3A'
I figured it out. My url had a : in it, and urllib cannot use that character. I replaced it with %3A and now it's working. Web browsers usually convert : to %3A automatically, but urllib requires it to be converted first.