how to make checkbox works fine in notebook, tkinter, matplotlib

I have 3 sheets in a notebook that do the same thing as I show in the code below. (This code works fine here but not in my code)

All sheets have the function checkbox_O and g_checkbox with the same name and all use the global variable lines

When I press the graph button, the graphs are displayed but the checkboxes only work fine on sheet 1.

I did code tests and I realize that, in sheet 2 and 3, the g_checkbox function does not have access to the lines array (I don't know why)

This is what I tried to fix it and it didn't work:

1. tried to write g_checkbox function as a class method
2. I tried to place a global lines variable for each sheet
3. I changed the name of the function checkbox_O in each sheet, so that it is different in each one of them

I need help please to know how to make the checkboxes work in all three sheets. I don't know what I'm doing wrong and I don't know how to fix it.

Thanks in advance

import numpy as np
import tkinter as tk
from tkinter import ttk
import matplotlib
from matplotlib import pyplot as plt
matplotlib.use('TkAgg')
from matplotlib.figure import Figure
from matplotlib.backends.backend_tkagg import(FigureCanvasTkAgg, NavigationToolbar2Tk)
from matplotlib import style
from matplotlib.widgets import CheckButtons, Button, TextBox, RadioButtons


x = np.arange(-15, 15, .01)
lines = []


class root(tk.Tk):
    def __init__(self):
        super().__init__() 
        self.geometry('750x618')
        self.my_book()
        
    def my_book(self):
        #I left it out so the code doesn't get too long
        

class myFrame(ttk.Frame):
    def __init__(self,  master=None):
        super().__init__(master)
        self.master = master
        self.my_widgets()

    
    def my_widgets(self):
        self.f = Figure(figsize=(7, 5.5), dpi=100)
        self.plott = self.f.add_subplot()
    
        self.canvas = FigureCanvasTkAgg(self.f, self)
        self.canvas.draw()
        self.canvas.get_tk_widget().pack()

        self.button_ax = self.f.add_axes([0.76, 0.95, 0.11, 0.04])
        self.button_graph = Button(self.button_ax, 'Graph', color='darkgrey')
        self.button_graph.on_clicked(self.callback_button)
        plt.show()

    def callback_button(self, event):
        self.graph_1()
        self.graph_2()

    def checkbox_O(self, lines, f):
        self.check_ax = f.add_axes([0.76, 0.085, 0.21, 0.16])
        labels = [str(line.get_label()) for line in lines]
        labels_visual = ['graph1', 'graph2']
        visibility = [line.get_visible() for line in lines]
        self.check = CheckButtons(self.check_ax, labels_visual, visibility)

        def g_checkbox(label):
            selec_index = [ind for ind, lab in enumerate(self.check.labels) if label in lab._text]
            for index, laabel in enumerate(labels):
                if laabel==label:
                    lines[index].set_visible(not lines[index].get_visible())
                    if (lines[index].get_visible()):
                        self.check.rectangles[selec_index[0]].set_fill(True)
                    else:
                        self.check.rectangles[selec_index[0]].set_fill(False)

            f.canvas.draw()
        self.check.on_clicked(g_checkbox)
        plt.show()

    def graph_1(self):
        global lines
        for i in range(0, 15):
            V = np.sin(i/10*x) + 2*i 
            l0, = self.plott.plot(x, V, label='graph1')
            lines.append(l0)
        self.checkbox_O(lines, self.f)
        
    def graph_2(self):
        global lines
        for i in range(0, 15):
            l0, = self.plott.plot([i, i], [0, 10], label='graph2')
            lines.append(l0)   
        self.checkbox_O(lines, self.f)
    
        
        
if __name__ == "__main__":
    app = root()
    app.mainloop()

PS: By the way, I took the code from stackoverflow and modified it so that it works like this