Multiplying and then summing values from two dictionaries (prices, stock)

Question

I need to multiply the values from each key and then add all the values together to print a single number. I know this probably super simple but i’m stuck

In my mind, I’d address this with something like:

for v in prices:
total = sum(v * (v in stock))
print total

But something like that isn’t going to work 🙂

prices = {
"banana": 4,
"apple": 2,
"orange": 1.5,
"pear": 3 }

stock = {
"banana": 6,
"apple": 0,
"orange": 32,
"pear": 15 }

Asked By: Rhys Isterix

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Source

Answer 1

If you would have known, how to iterate through a dictionary, index a dictionary using key and comprehend a dictionary, it would be a straight forward

>>> total = {key: price * stock[key] for key, price in prices.items()}
>>> total
{'orange': 48.0, 'pear': 45, 'banana': 24, 'apple': 0}

Even if your implementation of Python does not provide Dictionary comprehension (< Py 2.7), you can pass it as a List Comprehension to the dict built-in

>>> dict((key, price * stock[key]) for key, price in prices.items())
{'orange': 48.0, 'pear': 45, 'banana': 24, 'apple': 0}

If you don;t want compatible between 2.X and 3.X you can also use iteritems instead of
items

{key: price * stock[key] for key, price in prices.iteritems()}

If you want a single total of the result, you can pass the individual products to sum

>>> sum(price * stock[key] for key, price in prices.items())
117.0

Answered By: Abhijit

Answer 2

You could use a dict comprehension if you wanted the individuals:

>>> {k: prices[k]*stock[k] for k in prices}
{'orange': 48.0, 'pear': 45, 'banana': 24, 'apple': 0}

Or go straight to the total:

>>> sum(prices[k]*stock[k] for k in prices)
117.0

Answered By: DSM

Answer 3

I’m guessing you’re on codeacademy? If so just do this:

total = 0
for key in prices:  
    prices = 53
    stock = 10.5
    total = prices + stock
print total

Unlike what the instructions said you would have to add all the values together before multiplying them and adding them to total. Hope this helps.

Answered By: The Rising Sun

Answer 4

total = 0   
for key in prices:
    print prices[key] * stock[key]
    total += prices[key] * stock[key]
print total

Answered By: Samko

Answer 5

Correct answer for codeacademy according to task description:

 prices = {
       "banana" : 4,
       "apple"  : 2,
       "orange" : 1.5,
       "pear"   : 3,
   }
   stock = {
        "banana" : 6,
        "apple"  : 0,
        "orange" : 32,
        "pear"   : 15,
    }

    for key in prices:
        print key
        print "price: %s" % prices[key]
        print "stock: %s" % stock[key]

     total = 0
     for key in prices:
        value = prices[key] * stock[key]
        print value
        total = total + value
    print total

Answered By: Alexander Petrov

Answer 6

I wrote the following code and it worked.
for key in prices:

print key
   print "price: %s" % + prices[key]
   print "stock: %s" % + stock[key]

for key in prices:
value = prices[key]*stock[key]
print value
total = total + value
print total

Answered By: Deirdre Brennan

Answer 7

Quick and general answer.

If you are looking for an efficient and fast way to multiply the elements (values) of two dictionaries together, do use dict comprehension.
Be sure the two dictionaries have the same keys.
You could use this one-liner:

new_dict = { key : value * dict2[key] for key,value in dict1.items() }

Answered By: Andrea Bragantini

Multiplying and then summing values from two dictionaries (prices, stock)

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