How to change a variable status in check button and use it in another function

I have a check button located in a main window. I need to use two functions when the check button is clicked. The first function opens a pop up and the second function changes the "activate_SPI" variable from "inactive" to "active". I want to use the "activate_SPI" status in another function that is called when I press the "compute" button in GUI to print "ok". However, I face the following error:

"NameError: name 'activate_SPI' is not defined"

How can I fix this error?

import pandas as pd
import numpy as np
from standard_precip import spi
import tkinter as tk
from tkinter import ttk
from tkinter import filedialog
from tkinter.messagebox import showinfo
import os
from matplotlib.backends.backend_tkagg import (FigureCanvasTkAgg, 
NavigationToolbar2Tk)
from tkinter import * 
from PIL import Image, ImageTk
class EGEDT(tk.Frame):
def __init__(self, master=None):
super().__init__(master)
self.master = master
self.pack()
self.create_widgets()
# dimensions of the main window
master.geometry("300x300")
def create_widgets(self):
self.top_frame = ttk.Frame(self)
padding_x = 8
padding_y = 7
self.working_dir = "/"
# Create a check button   
self.ab_frame = ttk.Frame(self.top_frame)
self.ab_label = ttk.Label(self.ab_frame, text="Select the check button:")
self.ab_label.grid(row=1, column=0, padx= 5, pady= 5)
var1 = tk.IntVar()
self.a = ttk.Checkbutton(self.ab_frame,text="SPI",variable=var1, onvalue=1, offvalue=0,command=lambda: [f() for f in [self.open_popup_SPI, self.func_activate_SPI]])
self.a.grid(row=2, column=1, padx= 0, pady= 0)
self.ab_frame.grid(row=2, column=0, sticky=tk.W, padx=padding_x, pady=padding_y)       
self.top_frame.grid(row=0, column=0)
# Output file widget
self.out_frame = ttk.Frame(self.top_frame)
self.out_label = ttk.Label(self.out_frame, text="Save : ")
self.out_label.grid(row=0, column=0, sticky=tk.W)
self.out_string = tk.StringVar()
self.out_entry = ttk.Entry(self.out_frame, width=7, textvariable=self.out_string)
self.out_entry.grid(row=1, column=0)
self.out_btn = ttk.Button(self.out_frame, width=7, text="...", command=self.out_file_selector)
self.out_btn.grid(row=1, column=1)
self.out_frame.grid(row=5, column=0, sticky=tk.W, padx=padding_x, pady=padding_y)
# Create ok button to save the SPI excek file into the hard drive
self.buttons = ttk.Frame(self.out_frame)
self.PDF = ttk.Button(self.out_frame, text="Compute", width=10, command=self.Compute_TI_model_and_Extract_EG)
self.PDF.grid(row=1, column=2)
self.buttons.grid(row=5, column=0, sticky=tk.E, padx=padding_x, pady=padding_y)
self.buttons = ttk.Frame(self.out_frame)
self.cancel = ttk.Button(self.buttons, text="Cancel", width=7, command=self.master.destroy)
self.cancel.grid(row=2, column=2)
self.buttons.grid(row=2, column=2, sticky=tk.E, padx=padding_x, pady=padding_y)
def open_popup_SPI(self):
top= Toplevel(self.top_frame)
top.geometry("750x250")
top.title("Child Window")
Label(top, text= "Hello World!", font=('Mistral 18 bold')).place(x=150,y=80)
activate_SPI = "inactive"
def func_activate_SPI(activate_SPI):
# global activate_SPI  
activate_SPI = "active"
def Geotiff_file_selector(self):
result = self.Geotiff_string.get()
result = filedialog.askopenfilename(initialdir = self.working_dir, title = "Select File", filetypes = (("Geotiff files","*.tif"),("all files","*.*")))
self.Geotiff_string.set(result)
self.working_dir = os.path.dirname(result)
def out_file_selector(self):
result = self.out_string.get()
result = filedialog.asksaveasfilename(initialdir = self.working_dir, title = "Save File", filetypes = (("Geotiff files","*.tif"),("all files","*.*")))
self.out_string.set(result)
self.working_dir = os.path.dirname(result)
def Compute_TI_model_and_Extract_EG(self):
if activate_SPI == 'active':
print('ok')
def main():
root = tk.Tk()   
root.title("Main window")
app = EGEDT(master=root)
app.mainloop()
main()

Since activate_SPI is a class variable, it is accessed by using EGEDT.activate_SPI.

However I would suggest to use an instance variable which replaces the local variable var1 instead:

class EGEDT(tk.Frame):
    ...
    def create_widgets(self):
        ...
        self.activate_SPI = tk.IntVar()  # replace var1

        self.a = ttk.Checkbutton(self.ab_frame, text="SPI", variable=self.activate_SPI, 
                                 onvalue=1, offvalue=0, command=self.open_popup_SPI)
        ...

    ...
    #activate_SPI = "inactive"   # don't use class variable

    # this function is not necessary at all
    def func_activate_SPI(self):
        pass

    ...
    def Compute_TI_model_and_Extract_EG(self):
        if self.activate_SPI.get():
            print("ok")