Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

Python Python Collections (2016, retired 2019) Lists Shopping List Take Three

Vinod Kumar
Vinod Kumar
944 Points

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

When below code executed getting TypeError:

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'

[MOD: added ```python formatting -cf]

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,166 Points

You have a typo in your assignment of psotion:

    except ValueError:
        psotion = None