Basically I've got this current url and this other key that I want to merge into a new url, but there are three different cases.

Suppose the current url is localhost:32401/A/B/foo

if key is bar then I want to return localhost:32401/A/B/bar

if key starts with a slash and is /A/bar then I want to return localhost:32401/A/bar

finally if key is its own independent url then I just want to return that key = htt p://foo.com/bar -> http://foo.com/bar

I assume there is a way to do at least the first two cases without manipulating the strings manually, but nothing jumped out at me immediately in the os.path module.