[$] Python virtual environments

In a short session at the 2018 Python Language Summit, Steve Dower broughtup the shortcomings of Python virtual environments,which are meant to create isolated installations of the language and itsmodules. He said his presentation was "co-written with Twitter" and,indeed, most of his slides were of tweets. At the end, he also slipped in anannouncement of his plans for hosting a core development sprint in September.