I do scientific programming / ml, and python3 is nothing but hassle. The resistance in my community, imo, is we got a medium pain (print vs print() isn't a hassle / dict.iteritems -> dict.items is a tiny pain, but dealing with years of split libraries and parallel installs and all that was a giant pita) with no benefits at all. Years later in 3.4 or 3.5 we finally got a matrix mult operator, but that's about it.