Python: Type Error unsupported operand type(s) for +: 'int' and 'str' - python-3.4

Question

I'm really stuck, I am currently reading Python - How to automate the boring stuff and I am doing one of the practice projects.
Why is it flagging an error? I know it's to do with the item_total.
import sys
stuff = {'Arrows':'12',
'Gold Coins':'42',
'Rope':'1',
'Torches':'6',
'Dagger':'1', }
def displayInventory(inventory):
print("Inventory:")
item_total = sum(stuff.values())
for k, v in inventory.items():
print(v + ' ' + k)
a = sum(stuff.values())
print("Total number of items: " + item_total)
displayInventory(stuff)
error i get:
Traceback (most recent call last):
File "C:/Users/Lewis/Dropbox/Python/Function displayInventory p120 v2.py", line 17, in
displayInventory(stuff)
File "C:/Users/Lewis/Dropbox/Python/Function displayInventory p120 v2.py", line 11, in displayInventory
item_total = int(sum(stuff.values()))
TypeError: unsupported operand type(s) for +: 'int' and 'str'

Answer 1

Your dictionary values are all strings:
stuff = {'Arrows':'12',
'Gold Coins':'42',
'Rope':'1',
'Torches':'6',
'Dagger':'1', }
yet you try to sum these strings:
item_total = sum(stuff.values())
sum() uses a starting value, an integer, of 0, so it is trying to use 0 + '12', and that's not a valid operation in Python:
>>> 0 + '12'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'str'
You'll have to convert all your values to integers; either to begin with, or when summing:
item_total = sum(map(int, stuff.values()))
You don't really need those values to be strings, so the better solution is to make the values integers:
stuff = {
'Arrows': 12,
'Gold Coins': 42,
'Rope': 1,
'Torches': 6,
'Dagger': 1,
}
and then adjust your inventory loop to convert those to strings when printing:
for k, v in inventory.items():
print(v + ' ' + str(k))
or better still:
for item, value in inventory.items():
print('{:12s} {:2d}'.format(item, value))
to produce aligned numbers with string formatting.

Answer 2

You are trying to sum a bunch of strings, which won't work. You need to convert the strings to numbers before you try to sum them:
item_total = sum(map(int, stuff.values()))
Alternatively, declare your values as integers to begin with instead of strings.

Answer 3

This error produce because you was trying sum('12', '42', ..), so you need to convert every elm to int
item_total = sum(stuff.values())
By
item_total = sum([int(k) for k in stuff.values()])

Answer 4

The error lies in line
a = sum(stuff.values())
and
item_total = sum(stuff.values())
The value type in your dictionary is str and not int, remember that + is concatenation between strings and addition operator between integers. Find the code below, should solve the error, converting it into int array from a str array is done by mapping
import sys
stuff = {'Arrows':'12',
'Gold Coins':'42',
'Rope':'1',
'Torches':'6',
'Dagger':'1'}
def displayInventory(inventory):
print("Inventory:")
item_total = (stuff.values())
item_total = sum(map(int, item_total))
for k, v in inventory.items():
print(v + ' ' + k)
print("Total number of items: " + str(item_total))
displayInventory(stuff)