My list has a huge bug but I don't get it :(

import os

def clear_screen():
    os.system("cls" if os.name == "nt" else "clear")



shopping_list = []


def add_to_list(item):
    show_list()
    if len(shopping_list):
        position = input("Where should i add {}?\n"
                         "Press ENTER to add to the end of the list\n"
                         "> ".format(item))
    else:
        position = 0

        try:
            position = abs(int(position))
        except ValueError:
            position = None
        if position is not None:
            shopping_list.insert(position-1,item)

        show_list()


    shopping_list.append(item)
    print("Added! List has {} items.".format(len(shopping_list)))
    show_list()



def show_help():
    clear_screen()
    print("What should we pick up at the store?")
    print("""
Enter 'DONE' to stop adding items.
Enter 'HELP' for this help.
Enter 'SHOW' to see your list.
""")


def show_list():
    clear_screen()


    print("This is on your bag:")

    index = 1
    for item in shopping_list:
        print("{}. {}".format(index,item))

    print("-"*10)

show_help()
while True:
    new_item = input("> ")

    if new_item.upper() == 'DONE' or new_item.upper() == 'QUIT': 
        break
    elif new_item.upper == 'HELP':
        show_help()
        continue
    elif new_item.upper == 'SHOW':
        show_list()
        continue
    else:
        add_to_list(new_item)


    add_to_list(new_item)