Look up Prices¶

In this chapter you will:¶

area	topic
🚀	write a better receipt assistant
⚙	define a dictionary
⚙	look up values of a dictionary
🔀	iterate through a list of dictionary keys
🔀	use lists as dictionary values
🐞	fix errors in dictionary definitions
🐞	fix index errors

Exercise 1: Look up¶

Consider we would like to look up shopping prices. In this chapter, we will use a dictionary, a data structure that is good for looking up items.

Execute the following code:

prices = {
   "apple": 0.50,
   "banana": 1.00,
   "orange": 1.50,
   "cherries": 3.00,
}
print(prices["banana"])

How does the dictionary differ from a list?

Exercise 2: Explore¶

Find out what each of the expressions does to the dictionary in the center.

Exercise 3: Look up¶

Now consider having the list of items in fruit. You would like to calculate the total price. For that, the list and dictionary need to work together.

Sort the lines and indent them properly:

print(total) total += prices[item] bought = ["banana", "banana", "cherries", "apple", "apple", "banana"] for item in bought: total = 0 prices = {

"apple": 0.50, "banana": 1.00, "orange": 1.50, "cherries": 3.00,

}

Exercise 4: Receipt assitant 2.0¶

Improve the receipt assistant from the previous chapter so that it uses a dictionary of prices.

Exercise 5: Traveler¶

The following program allows you to travel from one city to the next. Unfortunately, it contains five bugs. Find and fix them.

cities = {
    "New York": ["Tokyo", "Delhi", "London"],
    "Poznan": ["London", "Berlin"],
    "London": ["New York", "Poznan"]
    "Berlin": ["Tokyo", "Poznan"],
    "Tokyo": ["New York" "Berlin"],
    "Delhi": ["Katmandu"]
    }

location = "Berlin"
print "\nYour task: fly to Katmandu\n"

while location in cities and location == 'Katmandu':
    print(f"You are in {location}")

print("There are flights to ", cities["location"])
location = input("Where would you like to travel?")

print("You have reached your destination")

Exercise 6: Zip¶

Simplify the following code using the function zip():

fruits = ["apple", "banana", "orange", "cherries"]
prices = [0.5, 1.0, 1.5, 3.0]

table = []
i = 0
while i < len(fruits):
    row = (fruits[i], prices[i])
    table.append(row)
    i += 1
print(table)

Try the expression:

for a, b in zip(fruits, prices):
    ...

Reflection Questions¶

How can you create a dictionary?
What data types can you use as keys of a dictionary?
What data types can you use as values of a dictionary?
How can you modify values in a dictionary?
Is it possible to run a for loop over a dictionary?