TypeError: can only concatenate list (not "str") to list

Question

I am trying to make an inventory program to use in an RPG. The program needs to be able to add and remove things and then add them to a list. This is what I have so far:

inventory=["sword","potion","armour","bow"]
print(inventory)
print("ncommands: use (remove) and pickup (add)")
selection=input("choose a command [use/pickup]")

if selection=="use":
    print(inventory)
    remove=input("What do you want to use? ")
    inventory.remove(remove)
    print(inventory)

elif selection=="pickup":
    print(inventory)
    add=input("What do you want to pickup? ")
    newinv=inventory+str(add)
    print(newinv)

When I run this and try to pick something up, I get this error:

Traceback (most recent call last):
  File "H:/Year 10/Computing/A453/Python Programs/inventory.py", line 15, in <module>
    newinv=inventory+str(add)
TypeError: can only concatenate list (not "str") to list

Does any one have a fix for this, it would be greatly appreciated.

Asked By: user2885647

||

Source

Answer 1

I think what you want to do is add a new item to your list, so you have change the line newinv=inventory+str(add) with this one:

newinv = inventory.append(add)

What you are doing now is trying to concatenate a list with a string which is an invalid operation in Python.

However I think what you want is to add and delete items from a list, in that case your if/else block should be:

if selection=="use":
    print(inventory)
    remove=input("What do you want to use? ")
    inventory.remove(remove)
    print(inventory)

elif selection=="pickup":
    print(inventory)
    add=input("What do you want to pickup? ")
    inventory.append(add)
    print(inventory)

You don’t need to build a new inventory list every time you add a new item.

Answered By: jabaldonedo

Answer 2

That’s not how to add an item to a string. This:

newinv=inventory+str(add)

Means you’re trying to concatenate a list and a string. To add an item to a list, use the list.append() method.

inventory.append(add) #adds a new item to inventory
print(inventory) #prints the new inventory

Hope this helps!

Answered By: aIKid

Answer 3

You can use:

newinv=inventory+[add]

but using append is better since it doesn’t create a new list:

inventory.append(add)

Answered By: alpere

Answer 4

Let me fix your code

inventory=["sword", "potion", "armour", "bow"]
print(inventory)
print("ncommands: use (remove) and pickup (add)")
selection=input("choose a command [use/pickup]")

if selection == "use":
    print(inventory)
    inventory.remove(input("What do you want to use? "))
    print(inventory)
elif selection == "pickup":
    print(inventory)
    add=input("What do you want to pickup? ")
    newinv=inventory+[str(add)] #use '[str(add)]' or list(str(add))
    print(newinv)

The error is you are adding string and list, you should use list or [] to make the string become list type

Answered By: user12066865

Answer 5

I have a solution for this. First thing that add is already having a string value as input() function by default takes the input as string. Second thing that you can use append method to append value of add variable in your list.

Please do check my code I have done some modification : –
{1} You can enter command in capital or small or mix
{2} If user entered wrong command then your program will ask to input command again

inventory = ["sword","potion","armour","bow"]
print(inventory)
print("ncommands : use (remove item) and pickup (add item)")
selection=input("choose a command [use/pickup] : ")
while True:
if selection.lower()=="use":
print(inventory)
remove_item=input("What do you want to use? ")
inventory.remove(remove_item)
print(inventory)
break

 elif selection.lower()=="pickup":
      print(inventory)
      add_item=input("What do you want to pickup? ")
      inventory.append(add_item)
      print(inventory)
      break
 
 else:
      print("Invalid Command. Please check your input")
      selection=input("Once again choose a command [use/pickup] : ")

Answered By: Aditya

TypeError: can only concatenate list (not "str") to list

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