If it might be of some use to you, I have the exact same Python 3 curve and surface fitting desktop application written in tkinter (https://bitbucket.org/zunzun

If it might be of some use to you, I have the exact same Python 3 curve and surface fitting desktop application written in tkinter (https://bitbucket.org/zunzuncode/tkinterFit https://bitbucket.org/zunzuncode/tkinterFit), pyQt5 (https://bitbucket.org/zunzuncode/pyQt5Fit https://bitbucket.org/zunzuncode/pyQt5Fit), pyGtk (https://bitbucket.org/zunzuncode/pyGtkFit https://bitbucket.org/zunzuncode/pyGtkFit), and wxPython (https://bitbucket.org/zunzuncode/wxPythonFit https://bitbucket.org/zunzuncode/wxPythonFit). All are BSD license.