AttributeError: 'NoneType' object has no attribute 'format'

import os


# make a list that will hold our items
shopping_list = []

print("What should we pick up at the store?")

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

def show_instructions():
    clear_screen()
    # print out instructions on how to use it
    print("")
    print("Enter done to stop adding stuff")
    print("Enter show to see your shopping list")
    print("Remove to delete an item from your list")
    print("Enter help to see these instructions again")

def show_list():
    # print out the list
    clear_screen()
    print("Here's your list")
    index = 1
    for item in shopping_list:
        print("{}. " + item).format(index)
        index+=1

    print("-" * 10)
    print("")

def add_item(item):
    shopping_list.append(item)
    print("Added {} to shopping list. Shopping list now has {} items.".format(item, len(shopping_list)))
    show_list()

def remove_item():
    show_list()
    print("What would you like to remove?")
    rem_item = input("> ")
    try:
        shopping_list.remove(rem_item)
    except ValueError:
        pass
    show_list()

show_instructions()

# ask for new items
while True:
    try:
        new_item = input("> ")

    except:
        print("sorry please use quotes around your item.")

    else:
        if new_item.upper() == "DONE" or new_item.upper() == "QUIT":
            show_list()
            break
        elif new_item.upper() == "HELP":
            show_instructions()
        elif new_item.upper() == "SHOW":
            show_list()
        elif new_item.upper() == "REMOVE":
            remove_item()
        else:
            add_item(new_item)