TypeError:TypeError: unsupported operand type(s) for -: 'str' and 'int'

import os

shopping_list = []

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

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

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

    show_list()    


def show_help():
    clear_screen()
    print("What should we pick up at the store?")
    print("""
    Enter 'DONE' to stop shoping.
    Enter 'HELP' for any help.
    Enter 'SHOWLIST' to review the items added to the list
    """)


def show_list():
    clear_screen()
    print("here your list")
    index = 1

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

    print("-"*10)


show_help()
while True:
    new_item = input("Please enter the item you want to buy ")

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


Error:
Where should i add butter?                                                                                                                     
Press ENTER to add to the list                                                                                                                 
>                                                                                                                                              
Traceback (most recent call last):                                                                                                             
  File "shoppinglist2.py", line 64, in <module>                                                                                                
    add_to_list(new_item)                                                                                                                      
  File "shoppinglist2.py", line 22, in add_to_list                                                                                             
    shopping_list.insert(int(position-1),item)                                                                                                 
TypeError: unsupported operand type(s) for -: 'str' and 'int'