As far as I can tell, the reason Qt5 Designer does not load custom PyQt5 widgets
is due to the 'stock' shared library libpyqt5.so (which comes with PyQt5) not
being built for the correct combination of the Python and Qt versions. It seems
the only way to get around this is to build PyQt5 from source so we will have a
libpyqt5.so that is correct and will be able to load the custom widgets.
I don't know if this is necessary, I already had it installed
$ sudo apt-get install libpython-dev
SIP is a Python/C++ bindings generator used to build the bindings for PyQt. Stretch seems to have SIP 4.18, but PyQt5.7.1 needs SIP 4.19, so build from source.
$ wget https://sourceforge.net/projects/pyqt/files/sip/sip-4.19/sip-4.19.tar.gz
$ tar xzvf sip-4.19.tar.gz
$ cd sip-4.19
$ python configure.py
$ make
$ sudo make install
On my system I have both Qt4 and Qt5 installed. But on stretch Qt4 is the default so we have to set up the environment to use Qt5 before trying to build PyQt5.
Make sure Qt5 is installed:
$ qtchooser -list-versions
Select the Qt version:
$ export QT_SELECT=qt5
Check qmake version:
$ qmake --version
This should say
QMake version 3.0
Using Qt version 5.7.1 in /usr/lib/x86_64-linux-gnu
$ wget https://sourceforge.net/projects/pyqt/files/PyQt5/PyQt-5.7.1/PyQt5_gpl-5.7.1.tar.gz
$ tar xzvf PyQt5_gpl-5.7.1.tar.gz
$ cd PyQt5_gpl-5.7.1
$ python configure.py
$ make
$ sudo make install
Use the PYQTDESIGNERPATH environment variable to tell QtDesiner where to look
for the plugins
$ export PYQTDESIGNERPATH='/path/to/plugin/directory/'
Launch Qt5 Designer
$ qtchooser -run-tool=designer -qt=5
https://www.ics.com/blog/integrating-python-based-custom-widget-qt-designer
https://harishnavnit.wordpress.com/2014/03/24/handling-multiple-versions-of-qt
I have found that qttools5.dev package must be present for the plugin to be made.
There is no good warning that this is a problem.
Chris M