I forgot to mention in my last comment that https://github.com/vetux/qcalculator https://github.com/vetux/qcalculator is also a nice qt based, exprtk using calc

I forgot to mention in my last comment that https://github.com/vetux/qcalculator https://github.com/vetux/qcalculator is also a nice qt based, exprtk using calculator with a python interface and higher floating point precision than plain exprtk.