The problem may not be a bug but a deliberate design choice. urllib is rather low level and doesn't implement some browser magic. Browsers handle stuff like 'ä' -> '%C3%A4', ' ' -> '%20' or IDNA but urllib doesn't. I always saw it as may responsibility to quote and encode everything myself. Higher level APIs such as requests are free to implement browser magic.

Contrary to common believes an URL with an umlaut or space is *not* a valid URI. From http://docs.python.org/3/library/urllib.request.html#urllib.request.Request

> url should be a string containing a valid URL.

I suggest that this ticket shall be closed as "won't fix".