def file_save():
f = tkFileDialog.asksaveasfile(mode='w', defaultextension=".txt")
if f is None: # asksaveasfile return `None` if dialog closed with "cancel".
return
text2save = str(text.get(1.0, END)) # starts from `1.0`, not `0.0`
f.write(text2save)
f.close()