🗂️ Dictionaries & Sets, lesson 2 of 5
Looping over dictionaries
Walk through keys, values and pairs, and count things with a dict.
11 min
2 exercises
2 quizzes
0/4 solved
Getting Python ready… examples can run in a moment.
Looping over a dict gives you its keys. Ask for other views when you need them:
d.keys(): the keysd.values(): the valuesd.items():(key, value)pairs, ready to unpack
Dicts remember the order keys were added.
Report card
Change the loop to for subject in grades:. What do you get?
The counting pattern. To count things, use the
thing as the key and the count as the value.
counts.get(word, 0) returns 0 the first time a
word appears, so there's no KeyError:
counts[word] = counts.get(word, 0) + 1
Word counter
Paste in a sentence of your own. Try text.lower().split() so "The" and "the" count together.
What does this print?
Best sales day
The same "track the best" pattern from loops, now with key and value together.
Changing size mid-loop
Change the loop to for item in list(stock): and it works.
What does this print?
Checkout total
cart maps each item to a quantity, and
prices maps items to a price. Loop over
cart.items() and add quantity * price for each
item to total.
Lunch vote
Count the votes into the tally dict (food → number
of votes) using the counting pattern. Then set
winner to the food with the most votes.