[Tkinter] Spawn sub-window with button press

[woooee]

See if this makes more sense. It also runs without errors.

import sys
if 3 == sys.version_info[0]: ## 3.X is default if dual system
    import tkinter as tk     ## Python 3.x
    from tkinter import ttk
else:
    import Tkinter as tk     ## Python 2.x
    import ttk

class MainWindow():
    def __init__(self, parent):
        self.parent=parent
        self.fr=ttk.Frame(parent)
        self.fr.grid(column=0, row=0, sticky='nsew')
        self.fr.columnconfigure(0, weight=1)
        self.fr.rowconfigure(0, weight=1)
        self.mem_exists = tk.StringVar()
        self.reg_scan = tk.StringVar()
        self.sub_win=None
        self.widgets()
 

    def delete_dmps(self):
        if self.sub_win:
            self.sub_win.destroy()

    def widgets(self):
        self.mem_labl1 = ttk.Label(self.fr, text='Memory Dumps:')
        self.mem_labl1.grid(column=0, row=0)
        self.mem_labl2 = ttk.Label(self.fr, textvariable=self.mem_exists)
        self.mem_labl2.grid(column=0, row=1)
        self.mem_buton = ttk.Button(self.fr, text='Delete', command=self.delete_dmps)
        self.mem_buton.grid(column=0, row=2)
        self.dmp_separ = ttk.Separator(self.fr, orient='horizontal')
        self.dmp_separ.grid(column=0, row=3, rowspan=1, sticky=('EW'))
        self.scn_labl1 = ttk.Label(self.fr, text='Scan for Dumps')
        self.scn_labl1.grid(column=0, row=4)
        self.scn_buton = ttk.Button(self.fr, text='Scan', command=self.scan_pressed)
        self.scn_buton.grid(column=0, row=5)
        self.vrt_separ = ttk.Separator(self.fr, orient='vertical')
        self.vrt_separ.grid(column=1, row=0, rowspan=6, sticky=('NS'))
        self.reg_labl1 = ttk.Label(self.fr, text='Unneeded Keys')
        self.reg_labl1.grid(column=2, row=0)
        self.reg_labl2 = ttk.Label(self.fr, textvariable=self.reg_scan)
        self.reg_labl2.grid(column=2, row=1)
##        self.reg_buton = ttk.Button(self.fr, text='Delete', command=self.delete_keys)
##        self.reg_buton.grid(column=2, row=2)
 
    def scan_pressed(self):
        self.sub_win = tk.Toplevel(self.parent) ##<----- ERROR HERE
##        self.write_dumps()
##        size = self.get_size()
##        self.mem_exists.set(f'{size} KB of memory dumps found!')

root=tk.Tk()
MW=MainWindow(root)
root.mainloop()