to be honest, I read "topk" as "topeka", but I am weird. While numpy doesn't use underscores all that much, I think this is one case where it makes sense.
I'd also watch out for the use of the term "sorted", as it may mean different things to different people, particularly with regards to what its default value should be. I also find myself initially confused by the names "largest" and "sorted", especially what should they mean with the "min-k" behavior. I think Dask's use of negative k is very pythonic and would help keep the namespace clean by avoiding the extra "min_k".
As for the indices, I am of two minds. On the one hand, I don't like polluting the namespace with extra functions. On the other hand, having a function that behaves differently based on a parameter is just fugly, although we do have a function that does this - np.unique().
Ben Root