Here is a calculator done with Python and QT5. This calculator will become PostX Gnu/Linux default and replace the current Java based one.
#QCalculator Copyright (c) 2018 JJ Posti <techtimejourney.net>
#QCalculator comes with ABSOLUTELY NO WARRANTY;
#for details see: http://www.gnu.org/copyleft/gpl.html.
#This is free software, and you are welcome to redistribute it under
#GPL Version 2, June 1991
Here is a screenshot + Download
v2: Centers text and fixes some really minor issues.