[Tutor] Finding the largest gap in tuple between two lists.

[Peter Otten]

Mats Wichmann wrote:

> 1. From an endpoint pair - say Buy/Levski and Sell/Olisar, you need the
> common items.  No point in looking further at items that can't both be
> bought at the source and sold at the destination.  Fortunately, Python
> sets are really good at this, but first you have to extract only the
> item names from your dictionary, since that comparison is based only on
> good names.  Something like this:
> 
> def common(curr, other):
>     return set(curr.keys()).intersection(set(other.keys()))

As dict.keys() are very similar to a set you can also write 

curr.keys() & other.keys()

or

curr.keys() & other  # if you don't care about symmetry ;)

> So one way to tackle this might be to build a new dictionary containing
> the items and their price difference. Given our previous idea of having
> a set which contains the common items:
> 
> prices = {k: Selling_Olisar[k] - Buying_Levski[k] for k in possibles}

While a dict is almost always a good idea there is no need to build one if 
you're only interested in one entry. Instead feed the pairs directly to 
max():

selling = dict(Selling_Olisar)
buying = dict(Buying_Levski)
possibles = selling.keys() & buying

if possibles:
    profit, good = max(
        (selling[k] - buying[k], k) for k in possibles
    )
    if profit > 0:
        print("Best good", good, "wins", profit, "per unit")
    else:
        print("Found nothing profitable.")
else:
    print("Found nothing that can be sold at your destination")