I’ve been stung by this too. Putting together parts of URLs for REST APIs without either missing or duplicate / separators [1] feels similar enough to the problem that os.path.join() solves [2] that I go looking for some kind of urljoin() function most likely in the urllib.parse namespace. When I find exactly the name I was looking for in the first place I expected to find it, I go ahh perfect until I try it and realise that it does something completely different.
I’ve since then discovered APIs that mandate all URLs have a trailing / and others that mandate the opposite which has shown me that there can never really be such a thing as a universal os.path.join()-like function for putting parts of a URL path together. But I do wish urljoin had been named something else.