Python3, difficulty with classes and tkinter - python-3.x

Question

First of all to kick it off,
I'm not great at programming,
I have difficulty with understanding most basics,
I always try doing my uterly best to solve things like this myself.
I'm trying to create a simple gui that makes json files. Everything works fine. Fine in the sense that I'm able to create the files.
Now I wanted to get my code cleaned up and to the next level. I have added tabs to the tkinter screen and that is where the troubles starts. Because when I'm, on a differend tab, the function doesn't get the current selected items, so I added buttons to save that list and then move to different tab.
I have a function(Save_List_t), which looks at the selected items from the listbox(a_lsb1) and saves them to a list(choice_list_t). This function runs when I press button(a_button).
After doing that I got a problem, I don't want to use "global" but I need the list in a other function(Mitre_Gen_Techs) to generate the files. This function runs when I press a button on the third tab.(c.button1)
To tackel this problem, I saw a post where someone uses a class to fix it. However even after reading to the documentation about classes I still don't truely get it.
Now I'm stuck and get the error. Which I don't find that strange, it makes sense to me why it gives the error but what am I doing wrong or how do I solve this issue.
The error:
Exception in Tkinter callback
Traceback (most recent call last):
File "C:\Users\thans\AppData\Local\Programs\Python\Python38-32\lib\tkinter\__init__.py", line 1883, in __call__
return self.func(*args)
TypeError: Save_List_t() missing 1 required positional argument: 'self'
The code I wrote:
from tkinter import *
from attackcti import attack_client
from mitretemplategen import *
from tkinter import ttk
# =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
# Mitre ATT&Ck
# =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ac = attack_client()
groups = ac.get_groups()
groups = ac.remove_revoked(groups)
techs = ac.get_enterprise_techniques()
techs = ac.remove_revoked(techs)
# =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
# Tkinter screen setup
# =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
root = Tk()
root.title("Mitre Att&ck")
root.minsize(900, 800)
root.wm_iconbitmap('')
# =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
# Functions / classes
# =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
class Screen(object):
def __init__(self):
self.choice_list_t = []
self.choice_list_g = []
def Save_List_t(self):
for item in a_lsb2.curselection():
self.choice_list_t.append(a_lsb2.get(item))
print(self.choice_list_t)
def Save_List_g(self):
choice_list_g = []
for item in b_lsb1.curselection():
self.choice_list_g.append(b_lsb1.get(item))
print(self.choice_list_g)
def Mitre_Gen_Techs(self):
# Gen the json file
# mitre_gen_techs(self.choice_list_t, techs)
#testing class
print(self.choice_list_t)
def Mitre_Gen_Groups(self):
# Gen the json file
# mitre_gen_groups(self.choice_list_g, groups)
#testing class
print(self.choice_list_g)
def main():
# =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
# First Tkinter tab
# =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
rows = 0
while rows < 50:
root.rowconfigure(rows, weight=1)
root.columnconfigure(rows, weight=1)
rows += 1
# Notebook creating tabs
nb = ttk.Notebook(root)
nb.grid(row=1, column=0, columnspan=50, rowspan=50, sticky='NESW')
# Create the differend tabs on the notebook
tab_one = Frame(nb)
nb.add(tab_one, text='APG')
tab_two = Frame(nb)
nb.add(tab_two, text='Actors')
tab_gen = Frame(nb)
nb.add(tab_gen, text='test')
# =-=- First Tab -=-=
# List box 1
a_lsb1 = Listbox(tab_one, height=30, width=30, selectmode=MULTIPLE)
# List with techs
a_lsb2 = Listbox(tab_one, height=30, width=30, selectmode=MULTIPLE)
for t in techs:
a_lsb2.insert(END, t['name'])
# Save list, to later use in Screen.Mitre_Gen_Techs
a_button = Button(tab_one, text="Save selected", command=Screen.Save_List_t)
# =-=- Second Tab -=-=
# List with TA's
b_lsb1 = Listbox(tab_two, height=30, width=30, selectmode=MULTIPLE)
for g in groups:
b_lsb1.insert(END, g['name'])
# Save list, to later use in Screen.Mitre_Gen_Groups
b_button = Button(tab_two, text="Save selected", command=Screen.Save_List_g)
# =-=- Third tab -=-=
c_button = Button(tab_gen, text="Print group json", command=Screen.Mitre_Gen_Groups)
c_button1 = Button(tab_gen, text="Print techs json", command=Screen.Mitre_Gen_Techs)
# Placing the items on the grid
a_lsb1.grid(row=1, column=1)
a_lsb2.grid(row=1, column=2)
b_lsb1.grid(row=1, column=1)
a_button.grid(row=2, column=1)
b_button.grid(row=2, column=1)
c_button.grid(row=2, column=1)
c_button1.grid(row=2, column=2)
root.mainloop()
# If main file then run: main()
if __name__ == "__main__":
main()
The application:
Image

Answer 1

I found someone who explained what was wrong.
Credits to Scriptman ( ^ , ^ ) /
simply adding:
sc = Screen()
And changing:
Button(tab_apg, text="Save selected", command=sc.Save_List_t)
Resolved the issue.