Not sure if url is still in 0.9 and works the same way, but would it be reasonable to exclude a parameter in the return value if its value is None?
Right now conditionally including a parameter requires making a dictionary beforehand and then modifying it, which makes a one-liner in kid a big mess (especially since kid doesn't seem to like competing curly braces, which a dictionary would introduce -- and using dict() for this purpose either requires more than one line since keyword arguments can't be expressions). Plus, having the string "None" as a parameter value (since it gets converted to string representation) isn't very useful anyway, I think, since it would be the same as just putting the string "None" itself.
