Okay, attached the patch based on your comment, Senthil Kumaran. Thanks.

The reason I use isinstance to check the type is because I want to support the inheritance as much as possible.

>>> class new_str(str):
...   pass
>>> urljoin(new_str('http://python.org') + new_str('hehe'))
will not work with the newest patch.

Also, in Lib/urllib/parse.py, most of the time, we use isinstance(x, str) not type(x) == str.

But I don't know. Maybe it does not matter.