When I run an application written in Python and Qt5 the looknfeel is quite ugly under KDE 5.x. Is there any way to make the application apply breeze's look?

What operating system, KDE, Qt versions are you using?

I've run into similar on Kubuntu 14.04 which still uses KDE 4 + Qt 4, but has Qt 5.2.1 available for running occasional Qt 5 applications (like jupyter qtconsole).
The version of breeze that I have installed is the KDE 4/Qt 4 version (built from scratch, I haven't tried also compiling it for Qt 5, but I don't think I'll get very far with that), so Qt5 applications can't use it directly. Instead I have it set up to use the gtk style and gtk set up to use gnome-breeze (also built from scratch using the github repo: https://github.com/dirruk1/gnome-breeze/).
The end result looks and feels ok, but is definitely far from optimal.