How to iterate over two dictionaries at once and get a result using values and keys from both

Question

def GetSale():#calculates expected sale value and returns info on the stock with              highest expected sale value
      global Prices
      global Exposure
              


        

Answer 1

The question is a bit vague, but answering the title, you can get both keys and values at the same time like this:

>>> d = {'a':5, 'b':6, 'c': 3}
>>> d2 = {'a':6, 'b':7, 'c': 3}
>>> for (k,v), (k2,v2) in zip(d.items(), d2.items()):
    print k, v
    print k2, v2


a 5
a 6
c 3
c 3
b 6
b 7

However, do mind that keys in dictionaries aren't ordered. Furthermore, if the two dictionaries do not contain the same number of keys, the code above will fail.

Answer 2

Looking at your problem, I would suggest you to create generator expression that navigates the two dictionary in pairs and using max with a custom key to calculate sale price to evaluate expected_sale_price and the corresponding stock

Sample Data

Prices = dict(zip(range(10), ((randint(1,100), randint(1,100)) for _ in range(10))))
Exposure = dict(zip(range(10), ((randint(1,100), randint(1,100)) for _ in range(10))))

Sample Code

def GetSale(Prices, Exposure):
    '''Get Sale does not need any globals if you pass the necessary variables as
       parameteres
    '''
    from itertools import izip
    def sale_price(args):
        '''
        Custom Key, used with the max function
        '''
        key, (bprice, cprice), (risk, shares) = args
        return ( (cprice - bprice ) - risk * cprice) * shares

    #Generator Function to traverse the dict in pairs
    #Each item is of the format (key, (bprice, cprice), (risk, shares))
    Price_Exposure = izip(Prices.keys(), Prices.values(), Exposure.values())


    #Expected sale price using `max` with custom key
    expected_sale_price = max(Price_Exposure, key = sale_price)
    key, (bprice, cprice), (risk, shares) =  expected_sale_price
    #The best stock is the key in the expected_sale_Price
    return "Stock {} with values bprice={}, cprice = {}, risk={} and shares={} has the highest expected sale value".format(key, bprice, cprice, risk, shares)

Answer 3

The question isn't well defined, and the answer accepted will fail for some dictionaries. It relies on key ordering, which isn't guaranteed. Adding additional keys to a dictionary, removing keys, or even the order they are added can affect the ordering.

A safer solution is to choose one dictionary, d in this case, to get the keys from, then use those to access the second dictionary:

d = {'a':5, 'b':6, 'c': 3}
d2 = {'a':6, 'b':7, 'c': 3}
[(k, d2[k], v) for k, v in d.items()]

Result:

[('b', 7, 6), ('a', 6, 5), ('c', 3, 3)]

This isn't more complex than the other answers, and is explicit about which keys are being accessed. If the dictionaries have different key orderings, say d2 = {'x': 3, 'b':7, 'c': 3, 'a':9}, consistent results are still given.