The python-vpython package needs a library that isn't pulled in during the dependency check. The package is the tk package. It is quite simple to solve, 'tk' just needs to be added into the depends section of the python-vpython PKGBUILD file. I checked python-vpython's PKGBUILD and tk wasn't in the depends section, confirming the problem. VPython won't run without the tk library. After I seperately installed tk through pacman, vpython started working flawlessly.