python: how to use dictionary and for loop to work out total cost for a list of (item, quantity) tup-CodePudding

this is my first time using stack overflow as I am just starting to learn python so apologies if I don't phrase things as clearly as I should!

I am working on a problem which asks me to set up a stationery shop. There is a dictionary with prices:

stationery_prices = {
    'pen': 0.55,
    'pencil': 1.55,
    'rubber': 2.55,
    'ruler': 3.55
}

I have to ask the user to input what item they would like and what quantity, and then arrange this in a list of tuples.

So now I have a list that looks like this:

[('pen', 1), ('pencil', 2)]

How do I use a for loop to refer back to the original dictionary of prices and add up the total cost for the user?

Thank you very much

CodePudding user response：

Iterate over each element, unpacking the tuple:

total = 0
for bought_item in bought_items:
    item_name = bought_item[0]
    quantity = bought_item[1]
    total  = stationery_prices[item_name] * quantity

print(total)

Note that this is more verbose than necessary (e.g. no tuple unpacking in the for loop). I chose to do this to reduce possible confusion with unfamiliar syntax. If you wanted to do it in one line, you could do:

total = sum(stationery_prices[item_name] * quantity 
    for item_name, quantity in bought_items)