The same graphical curve fitting and surface fitting application coded in four different Python3 GUI frameworks, with code on GitHub:

tkinter https://github.com/zunzun/tkInterFit

pyQt5 https://github.com/zunzun/pyQt5Fit

pyGtk https://github.com/zunzun/pyGtkFit

wxPython https://github.com/zunzun/wxPythonFit