FAQ: Learn Python: Python Lists and Dictionaries - It's Dangerous to Go Alone! Take This

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3 posts were split to a new topic: Shorthand to Increase a Variable’s Value?

2 posts were split to a new topic: “AttributeError: ‘NoneType’ Object Has No Attribute ‘remove’.”

I know I must have missed something earlier or am not completely getting all the concepts but rather than put in additional code that asks to adjust/add/remove values,items, keys or variables why not just change the original code why create so much additional lines?


I don’t quite get this code:
inventory['gold'] = inventory['gold'] + 50

How does it know to add 50 to the value (500)? Shouldn’t this just add 50 to the key (gold)

Were you able to solve the problem?

inventory = {
‘gold’ : 500,
‘pouch’ : [‘flint’, ‘twine’, ‘gemstone’], # Assigned a new list to ‘pouch’ key
‘backpack’ : [‘xylophone’,‘dagger’, ‘bedroll’,‘bread loaf’]

inventory[‘burlap bag’] = [‘apple’, ‘small ruby’, ‘three-toed sloth’]


inventory[‘pocket’] = [‘seashell’, ‘strange berry’, ‘lint’]
inventory[‘gold’] = inventory[‘gold’] + 50

Hey! Is there something we can help you with?

So you can either use:
inventory[‘gold’] = inventory[‘gold’] + 50
inventory[‘gold’ += 50.

Than why isnt it for remove:
inventory[‘backpack’] -= ‘dagger’

1 Like

The value keyed to “gold” is an integer, which responds to the operators + and - in the expected way.

The value keyed to “backpack” is a list of strings. You can “add” (concatenate) a list to a list, or a string to a string using the + operator, but the - operator will throw a TypeError if used with them.

lst = ['abc', 'def', 'gh']
lst = lst + ['ijk']
lst = lst - ['ijk']

# Output:
['abc', 'def', 'gh', 'ijk']
Traceback (most recent call last):
  File "C:\path\to\test.py", line 4, in <module>
    lst = lst - ['ijk']
TypeError: unsupported operand type(s) for -: 'list' and 'list'

Can you possible use the for item in list function to add 50 gold to the inventory? I tried it but at best got an error called Can't assign to literal.

I originally thought the instructions were to add the number 50 to gold so I typed in:


and it threw back an error saying:

Traceback (most recent call last):
File “python”, line 20, in
AttributeError: ‘int’ object has no attribute ‘append’

Then I realized I wasn’t doing what it wanted anyway and so put in the right code no problem. But now I’m sitting here wondering why the append function isn’t working and what would work in this case?

Edit: To clarify, I want to add the number 50 to the list. So gold would show 500, 50; not 550