I am currently setting up Python on my new Windows 10 machine. I have installed Python 2.7.15 and 3.6.1 (both of which I currently still need for different applications, installing from installers that I have previously successfully used on my previous Windows7 machine) and some packages via pip. Both Python installations are 32 bit.
One of those packages is PyQt5 (which only exists for Python3, anyway).
Now, I am trying to run one of my Python3 scripts which uses PyQt5 and I get 
"ImportError: DLL load failed: %1 is not a valid Win32 application." on the first line importing PyQt5.
I have tried using both pip install PyQt as well as py -3.6-32 -m pip install PyQt5 (after I found that this probably means an 32 bit/64 bit incompatibility between Python and the package). Neither solved the problem.
Does anyone have an idea what else I can try?
Restarting the machine several times seems to have solved the issue. (There were no changes after the first reboot, but after the second reboot it worked.)
Installing PyQt5 in Windows10 32bit Python3