From documentation:
"Construct a full (“absolute”) URL by combining a “base URL” (base) with another URL (url). Informally, this uses components of the base URL, in particular the addressing scheme, the network location and (part of) the path, to provide missing components in the relative URL."

base = http://www.example.com/example/foo.php?param=10
url = bar.php

I am expecting this result:
http://www.example.com/example/bar.php?param=10

But real result is:
http://www.example.com/example/bar.php

This should be easy fixable. Right now query= bquery is done only in one case - when path and params are empty.

I think that
if not query:
    query = bquery
should be moved before query might be used for first time. that means above code should be right after these lines:
if scheme != bscheme or scheme not in uses_relative:
    return url