I'm getting Traceback errors when I run the program and give a number where I would like something on my shopping 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 add_to_list(item):
    show_list()
    if len(shopping_list):
        position = input("Where should I add {} in?\n"
                         "Press ENTER to add to the end of the list\n"
                         "> ".format(item))
    else:
        position = 0

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


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()

Here's your list:                                                                                                           
1. apples                                                                                                                   
2. bananas                                                                                                                  
3. pizza                                                                                                                    
----------                                                                                                                  
Where should I add pears in?                                                                                                
Press ENTER to add to the end of the list                                                                                   
> 2                                                                                                                         
Traceback (most recent call last):                                                                                          
  File "shopping_list_3.py", line 64, in <module>                                                                           
    add_to_list(new_item)                                                                                                   
  File "shopping_list_3.py", line 32, in add_to_list                                                                        
    shopping_list.insert(position-1, item)                                                                                  
TypeError: unsupported operand type(s) for -: 'str' and 'int'