old_contents: import tkinter as tk
  import tk_tools
  
  root = tk.Tk()
  
  handle = tk_tools.SpreadSheetReader(root,
                                      path='./ref/test_data.xlsx',
                                      sheetname='Data entry')
  handle.grid()
  
  root.mainloop()
  
new_contents: import tkinter as tk
  import tk_tools
  
  
  if __name__ == '__main__':
  
      root = tk.Tk()
  
      sheet_handle = tk_tools.SpreadSheetReader(root,
                                                path='./ref/test_data.xlsx',
                                                sheetname='Data entry')
      sheet_handle.grid()
  
      root.mainloop()
  
subject: add if __name__ == '__main__':, renamed one variable.