Thanks Eryk, but I'm afraid I didn't follow most of what you said in your post.  As an end-user, I just wanted to be able to install the packages, import them, and then use within Python.  It is still not clear to me whether this is a problem with Python3, or a Matplotlib/Seaborn problem (and if it is the latter, are those folks informed?)

Do you need me to do any further tests with your patch - if so, kindly give detailed step-by-step instructions.  If not, please confirm that your patch will simply be incorporated in future releases of Python3, so that users wouldn't have to resort to the "one line patch" mentioned in my very first post.  Thanks for all your help!