This is primarily just a heads-up in case it was missed...
... since the Qt project enabled QtWebkit's Javascript JIT, starting with Qt5 (and PyQt5, etc), it now requires libselinux (the selinux library) to link and to run, which Slackware obviously does not have!
Alien Bob has come to the rescue - once again! - with a package:
http://www.slackware.com/~alien/slackbu ... kg64/14.2/
However, the above alone does not appear to work for PyQt5. (Not so far...)
If, as an alternative, PyQt5 is installed with pip or similar (instead from the system's own packages), then there is the issue of the nVidia drivers' incompatibility (bug), in both cases, nVidia's own and the nouveau driver. (With Intel Graphics this later method works fine. AMD??... No clue.)
There are some signs that a couple of major vendors are at least contemplating to include the minimum necessary selinux components (or the whole) in future releases but for now it is wait-and-see.
Consequently, this issue is unlikely to go away anytime soon, so one may wish to take a note of it.
p.s. This may require some emphasis; The PyQt (wheels) are broken with the nVidia drivers, independently from the Qt5 WebKit issue. However, that issue alone can be easily fixed by Not using PyQt wheels but instead resorting to a different distribution, like Continuum's Anaconda or use a different video card. Thus, video driver issue solved!
The libselinux issue, however, is not that simple! - No magic solution there.