ImportError:...Polar

I think the thing to do is to completely remove

    > site-pacages/matplotlib, then reinstall. I think.

Yep, that's guaranteed to fix it. We see this kind of error all the
time when a module that was formerly python becomes replaced by
an extension code module with the same name (or vice-versa, I'm not
sure). When you install a new mpl over an old one and you have for
examples transforms.pyd and transforms.py, the wrong one is chosen and
you get the import error.

Danny, judging by the fact that you are seeing this in the transforms
module, my guess is you haven't upgraded matplotlib in a long time, so
you should be pleasantly surprised by better performance in certain
areas.

JDH