python – how to add functions to menu my code makes a pizza menu in the terminal

hello I am creating a python menu it is about a pizza menu and I need help I do not know how to add some functions such as getting discounts in my code and postcode and address of a customer and phone number and email can you please help me her is the code that i have started with

def mainMenu():
    print("""
    1. Margareta pizza
    2. chilli pizza
    3. chicken pizza
    4. mushroom pizza
    5. pinapple pizza
    6. extra cheese margareta
    7. no cheese pizza
    8. Garlic bread
    9. large fries
    10. medium fries
    11. Medium fanta
    12. large fant
    13. medium coke
    14. large coke
    15. Esspreso
    16. cappaccino
    17. lemmon water
    18. flavoured water
    19. miniral sparkiling water
    20. miniral still water
    21. miniral spring water
    22. exit""")
    while True:
        try:
            selection=int(input("Enter choice:"))
            if selection==1:
                Margareta()
                break
               
            elif selection==2:
                chilli_pizza()
                break

            elif selection==3:
                chicken_pizza()
                break

            elif selection==4:
                mushroom_pizza()
                break

            elif selection==5:
                pinapple_pizza()
                break

            elif selection==6:
                extra_cheese_margareta()
                break

            elif selection==7:
                no_cheese_pizza()
                break

            elif selection==8:
                Garlic_bread()
                break
               
            elif selection==9:
                large_fries()
                break

            elif selection==10:
                medium_fries()
                break

            elif selection==11:
                Medium_fanta()
                break

            elif selection==12:
                large_fanta()
                break

            elif selection==13:
                medium_coke()
                break

            elif selection==14:
                large_coke()
                break

            elif selection==15:
                Esspreso()
                break

            elif selection==16:
                cappaccino()
                break

            elif selection==17:
                lemmon_water()
                break

            elif selection==18:
                flavoured_water()
                break

            elif selection==19:
                miniral_sparkiling_water()
                break

            elif selection==20:
                miniral_still_water()
                break

            elif selection==21:
                miniral_spring_water()
                break

            elif selection==22:
                break

            else:
                print("Invaliad option. Enter 1-22")
                mainMenu()
        except ValueError:
            print("Invaliad choice choose 1-22")
    exit


def Margareta():
    print("youre pizza is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def chilli_pizza():
    print("youre pizza is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def chicken_pizza():
    print("youre pizza is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def mushroom_pizza():
    print("youre pizza is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def pinapple_pizza():
    print("youre pizza is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def extra_cheese_margareta():
    print("youre pizza is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def no_cheese_pizza():
    print("youre pizza is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def Garlic_bread():
    print("youre garlic bread is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def large_fries():
    print("youre large fries is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def medium_fries():
    print("youre medium fries is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def Medium_fanta():
    print("youre fanta is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def large_fanta():
    print("youre large fanta is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def medium_coke():
    print("youre coke is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def large_coke():
    print("youre large coke is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def Esspreso():
    print("youre Esspresso is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def cappaccino():
    print("youre cappaccino is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def lemmon_water():
    print("youre water is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def flavoured_water():
    print("youre flavoured water is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def miniral_sparkiling_water():
    print("youre miniral sparkiling water is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def miniral_still_water():
    print("youre minaral still water is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()

def miniral_spring_water():
    print("youre miniral spring water is on its way")
    anykey=input("Enter anything to return to main menu")
    mainMenu()


   
    # main routine
mainMenu()