The reason I complain about that err() example is because it relies on very un-pythonic behavior. You're one stray comma away from sending in a tuple rather than a silently concatenated string.

(Coincidentally, this is why the separator there is a dash, rather than the more grammatically correct comma)

And I thank you for the other examples of ways to handle the URL, but again we've moved into making changes for very minor benefit just to please the analyzer, rather than the human reading the code.