How to break out of a for loop on button press?

[philipbergwerf]

from tkinter import *

# root
root = Tk()
root.title('SeqTank')
scrwidth = root.winfo_screenwidth()
scrheight = root.winfo_screenheight()
root.geometry("%sx%s+%s+%s" % (int(scrwidth / 1.5), 
                                int(scrheight / 1.25), 
                                int(scrwidth / 6), 
                                int(scrheight / 12)))
root.update()

# paned master with two panels
panedmaster = PanedWindow(root, orient='v', sashwidth=1, relief='flat', sashcursor='arrow', bg='#666666')
panedmaster.place(relwidth=1, relheight=1)
uppanel = PanedWindow(panedmaster, height=35, relief='flat')
panedmaster.add(uppanel)
downpanel = PanedWindow(panedmaster, relief='flat')
panedmaster.add(downpanel)

text_editor = Text(downpanel, 
                    bg='black', 
                    fg='#32a852',
                    insertbackground='white',
                    font=('Courier', 24))
text_editor.place(relwidth=1, 
                    relheight=1)
text_editor.focus_set()


generate_button = Button(uppanel, text='Play!')
generate_button.place(relwidth=1)

def process():
	for i in range(100):
		...
		# playing a midi-file here


generate_button.configure(command=process)

root.mainloop()

This is my simple tkinter interface. I created a little tool that generates a midi-file based on the text input(it uses a special lilypond-like syntax) and plays the midi file using mido in a for loop. My question is how can I break the for loop if I press the play button again before it finished the for loop? I hope someone can tell me in (regarding the above example) how I should write it different...