This would be good functionality to have, but there are some style idiosyncracies: extensive use of backslash continuations, sometimes with some odd indentation, and consistent use of the assert statement for checking inputs. Maybe the thing to do is to go ahead and merge it, with the addition of a TODO comment flagging the desirability of changing the style.

I think the second commit, merging master into the topic branch, is not a good idea--it will lead to a confusing history, will it not?

Hmm, I have no idea how that merge happened but clearly it is a bad idea. I am going to close this pull request and reopen a new one. On the style issues, I've asked Kevin to get started with github and mpl development workflow and he is working his way through it but is a first time user. So he will be happy to contribute some cleanup but I agree we can merge in the (fixed) pull request and let him clean from master.