purchase$($self$,$ item, qty$=1)$

Attempts to buy something from the vending machine. Before completing the purchase, check to

make sure the item is valid, there is enough stock of said item, and there is enough balance.

Output $($in order of priority$)$

str

$$Invalid item$$ if the item id is invalid $($Highest priority$)$

$$Machine out of stock$$ is returned if the machine is out of stock for all items

$$Item out of stock$$ is returned if there is no stock left of requested item.

$$Current item$\_$id stock: stock, try again$$ if there is not enough stock

$$Please deposit $remaining$$ if there is not enough balance

$$Item dispensed$$ if there is no money to give back to the user

$$Item dispensed, take your $change back$$ if there is change to give back

deposit$($self$,$ amount$)$

Deposits money into the vending machine, adding it to the current balance.

Output

str $$Balance: $balance$$ when machine is stocked

$$Machine out of stock. Take your $amount back$$ if the machine is out of stock.

$\_$restock$($self$,$ item, stock$)$

A protected method that adds stock to the vending machine. Note that when the VendingMachine

runs out of a product, a Vendor object will trigger the operation using its restock method $($already

implemented for you$)$

Output

str $$Current item stock: stock$$ for existing id

$$Invalid item$$ is returned if the item id is invalid.

isStocked$($self$)$

A property method $($behaves like an attribute$)$ that returns True if any item has any nonzero stock,

and False if all items have no stock.

Output

bool Status of the vending machine.

getStock$($self$)$

A property method $($behaves like an attribute$)$ that gets the current stock status of the machine.

Returns a dictionary where the key is the item and the value is the list $[$price$,$ stock$].$

Output

dict Current stock status represented as a dictionary.