Only by moving aside dvips(1) from MacPorts texlive-basic and using dvips(1) from MacTeX 2016 distribution, was I able to upgrade to MacPorts asymptote 2.41 vector graphics package.
asymptote 2.40 was installed about a month ago without any issues. Anyone care to confirm or dispute this claim? texlive-basic doesn’t appear to have been updated since December 2016, so it doesn’t make a lot of sense, but I’ve verified the problem and solution on two independent systems… Thank you! MacOS 10.12.4, Xcode 8.3.1, MacPorts via git HEAD. -AM
