How to set/unset checkbutton in popup menu

I'm banging around on a Python Tkinter gui. It's basically a bunch of text grouped into multiple columns. I have a popup menu that is displayed when the user right clicks any label in the top row. My popup menu has 3 options: Show All, Hide All, Expand On Change. The Expand On Change is a checkbutton. Here's my problem I can't get the set/unset the checkbutton on a column-by-column basis.

I've tied adding a variable when adding the checkbutton to the menu, and then setting that variable in the menu_popup function based on a boolean

show_checkmark = None


def menu_popup(event, fset):
  global current_flag_set
  global show_checkmark
  current_flag_set = fset
  show_checkmark = current_flag_set.expand_on_change
  try:
      popup.tk_popup(event.x_root, event.y_root)
  finally:
      popup.grab_release()

if __name__ == "__main__":
  root = tk.Tk()
  root.geometry('1024x768')

  show_checkmark = tk.IntVar(root, value=True)
  popup = tk.Menu(root, tearoff=0)
  popup.add_command(label='Show All', command=show_all)
  popup.add_command(label='Hide All', command=hide_all)
  popup.add_checkbutton(label='Expand On Change', command=toggle_expand_on_change, variable=show_checkmark)
  
  label_frame = tk.LabelFrame(root)
  label_frame.pack(expand='yes', fill='both')
  label_frame.bind(popup)

  # code that pulls the column headers from a file
  # loop to get column headers
      label = tk.Label(label_frame, text=t.capitalize(), font='Bold')
      flag_set = BoolSet(label, r, c)
      label.grid(row=r, column=c)
      label.bind("<Button-3>", lambda event, fset=flag_set: menu_popup(event, fset))

I suppose that current_flag_set.expand_on_change is a boolean.
<br>You should probably use set methode like this :

show_checkmark.set(current_flag_set.expand_on_change)