I got NameError while inserting item in the list

import os

shopping_list = []

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


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 current list.
""")

def show_list():
    clear_screen()
    print("Here's your list:")

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

    print("-"*10)

def add_to_list(new_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:
        # NameError happen here (maybe, if I'm not wrong)
        shopping_list.insert(position-1, item)  
    else:
        shopping_list.append(new_item)

    show_list()




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)

show_list()