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Python

BRIAN WEBER
BRIAN WEBER
21,570 Points
Posted by BRIAN WEBER
BRIAN WEBER
21,570 Points

Extra Credit Help Lists Redux (Move Items from One Position to Another)

Hello everyone. I am attempting the extra credit for the Lists Redux section under Python Collections. I have completed the CLEAR command part, but I am having trouble with moving items from one position to another. First off, when I prompt for user input for which item number the user wants to move I receive an error at idx_new. I am not sure how to format the input method to place an item at a certain index within a list to display. As for the "MOVE" code, I think it may be right, but I haven't got past the idx_new error. Below is the code I have (for some reason I cannot post the code to be formatted correctly like the other posts that I have seen):

Any help would be greatly appreciated!!!

Thanks,

Brian

BRIAN WEBER
BRIAN WEBER
21,570 Points
BRIAN WEBER
BRIAN WEBER
21,570 Points

I went ahead and formatted the code here in my previous post.

shopping_list = []


def remove_item(idx):
  index = idx - 1
  item = shopping_list.pop(index)
  print("Removed {}.".format(item))

def clear_list():
  shopping_list.clear()
  print("\nShopping list is cleared!")

def move_item(old_index,new_index):
  item_to_move = shopping_list[old_index]
  item = shopping_list.insert(new_index, item_to_move)

def show_help():
  print("\nSeparate each item with a comma.")
  print("Type DONE to quit, SHOW to see the current list, REMOVE to delete an item, MOVE an item and HELP to get this message.")


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

print("Give me a list of things you want to shop for.")
show_help()

while True:
  new_stuff = input("> ")

  if new_stuff == "DONE":
    print("\nHere's your list: ")
    show_list()
    break
  elif new_stuff == "HELP":
    show_help()
    continue
  elif new_stuff == "SHOW":
    show_list()
    continue
  elif new_stuff == "REMOVE":
    show_list()
    idx = input("Which item? Tell me the number.")
    remove_item(int(idx))
  elif new_stuff == "CLEAR":
    clear_list()
    continue
  elif new_stuff == "MOVE":
    if len(shopping_list) == 0:
      print("\nThere are no items in your shopping list.")
      show_help()
    else:
      show_list()
      idx_old = input("\nGive me the number of the item you want to move: ")
      old_index = idx_old - 1
      idx_new = input("\nWhere do you want to place the ", shopping_list[old_index], "?")
      new_index = idx_new - 1
      move_item(old_index, new_index)
  else:
    new_list = new_stuff.split(",")
    index = input("Add this at a certain spot? Press enter for the end of the list, or give me a number, Currently {} items in the list.".format(len(shopping_list)))
    if index:
      try:
        spot = int(index) - 1
        for item in new_list:
          shopping_list.insert(spot, item.strip())
          spot += 1
      except:
        print("\nCan only accept a number. Currently there are {} items in the shopping list".format(len(shopping_list)))
    else:
      for item in new_list:
        shopping_list.append(item.strip())
Devin Bartley
Devin Bartley
2,800 Points
Devin Bartley
Devin Bartley
2,800 Points

Hi Brian,

I can at least help you at least with the formatting. if you scroll to the bottom of the comments there is a Markdown Cheatsheet that shows you how to do the markups to separate the code. You should add 3 back ticks at the top line and 3 back ticks on the bottom line. If you add "python" after the back ticks at the top line it will highlight correctly.

Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

The type of error you received is important. Is it an IndexError meaning the index used for the shopping_list prompt is causing the error? Do you bounds check the old_index to be sure it is a valid value.

Along with fixing your formatting, please include the error thrown.

2 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

Formatting your code:

shopping_list = []

def remove_item(idx):
    index = idx - 1
    item = shopping_list.pop(index)
    print("Removed {}.".format(item))

def clear_list():
    shopping_list.clear()
    print("\nShopping list is cleared!")

def move_item(old_index,new_index):
    item_to_move = shopping_list[old_index]
    item = shopping_list.insert(new_index, item_to_move)

def show_help():
    print("\nSeparate each item with a comma.")
    print("Type DONE to quit, SHOW to see the current list, REMOVE to delete an item, MOVE an item and HELP to get this message.")

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

print("Give me a list of things you want to shop for.")
show_help()

while True:
    new_stuff = input("> ")
    if new_stuff == "DONE":
        print("\nHere's your list: ")
        show_list()
        break
    elif new_stuff == "HELP":
        show_help()
        continue
    elif new_stuff == "SHOW":
        show_list()
        continue
    elif new_stuff == "REMOVE":
        show_list()
        idx = input("Which item? Tell me the number.")
        remove_item(int(idx))
    elif new_stuff == "CLEAR":
        clear_list()
        continue
    elif new_stuff == "MOVE":
        if len(shopping_list) == 0:
            print("\nThere are no items in your shopping list.")
            show_help()
        else:
            show_list()
            idx_old = input("\nGive me the number of the item you want to move: ")
            old_index = idx_old - 1
            idx_new = input("\nWhere do you want to place the ", shopping_list[old_index], "?")
            new_index = idx_new - 1
            move_item(old_index, new_index)
    else:
        new_list = new_stuff.split(",")
        index = input("Add this at a certain spot? Press enter for the end of the list, or give me a number, Currently {} items in the list.".format(len(shopping_list)))
        if index:
            try:
                spot = int(index) - 1
                for item in new_list:
                    shopping_list.insert(spot, item.strip())
                    spot += 1
            except:
                print("\nCan only accept a number. Currently there are {} items in the shopping list".format(len(shopping_list)))
        else:
            for item in new_list:
                shopping_list.append(item.strip())

When running in a local file shop.py, I get the error:

Give me the number of the item you want to move: 1
Traceback (most recent call last):
  File "shop.py", line 56, in <module>
    old_index = idx_old - 1
TypeError: unsupported operand type(s) for -: 'str' and 'int'

input() returns a string. You need to wrap idx_old and idx_newin an int() function:

    old_index = int(idx_old) - 1
    ...
    new_index = int(idx_new) - 1

Once this was fixed, I notice that your second input prompt threw an error. input() takes a single argument. Using comma give it three. Change the commas to pluses +, or better yet, use a formatted string:

            idx_new = input("\nWhere do you want to place the {}?".format(shopping_list[old_index]))

One other error I noticed, after a MOVE, the item was in the new location, but also still in the old location.

BRIAN WEBER
BRIAN WEBER
21,570 Points
BRIAN WEBER
BRIAN WEBER
21,570 Points

Devin and Chris thank you for your help regarding formatting the code and fixing my code for the aforementioned errors. It seems to be working fine now.

shopping_list = []


def remove_item(idx):
  index = idx - 1
  item = shopping_list.pop(index)
  print("Removed {}.".format(item))

def clear_list():
  shopping_list.clear()
  print("\nShopping list is cleared!")

def move_item(old_index,new_index):
  item = shopping_list.insert(new_index, shopping_list.pop(old_index))

def show_help():
  print("\nSeparate each item with a comma.")
  print("Type DONE to quit, SHOW to see the current list, REMOVE to delete an item, MOVE an item and HELP to get this message.")


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

print("Give me a list of things you want to shop for.")
show_help()

while True:
  new_stuff = input("> ")

  if new_stuff == "DONE":
    print("\nHere's your list: ")
    show_list()
    break
  elif new_stuff == "HELP":
    show_help()
    continue
  elif new_stuff == "SHOW":
    show_list()
    continue
  elif new_stuff == "REMOVE":
    show_list()
    idx = input("Which item? Tell me the number.")
    remove_item(int(idx))
  elif new_stuff == "CLEAR":
    clear_list()
    continue
  elif new_stuff == "MOVE":
    if len(shopping_list) == 0:
      print("\nThere are no items in your shopping list.")
      show_help()
    else:
      show_list()
      idx_old = input("\nGive me the number of the item you want to move: ")
      old_index = int(idx_old) - 1
      idx_new = input("\nWhere do you want to place the " + shopping_list[old_index] + "?")
      # or idx_new = input("\nWhere do you want to place the {}?".format(shopping_list[old_index]))
      new_index = int(idx_new) - 1
      move_item(old_index, new_index)
  else:
    new_list = new_stuff.split(",")
    index = input("Add this at a certain spot? Press enter for the end of the list, or give me a number, Currently {} items in the list.".format(len(shopping_list)))
    if index:
      try:
        spot = int(index) - 1
        for item in new_list:
          shopping_list.insert(spot, item.strip())
          spot += 1
      except:
        print("\nCan only accept a number. Currently there are {} items in the shopping list".format(len(shopping_list)))
    else:
      for item in new_list:
        shopping_list.append(item.strip())

To fix the problem where after a MOVE, the item was in the new location, but also still in the old location: I forgot to add the pop method for the item to insert. The correct code is below.

def move_item(old_index,new_index):
  item = shopping_list.insert(new_index, shopping_list.pop(old_index))

Thanks again guys for your speedy responses!!