A level · 8 exercises

Python dictionaries

A dictionary links keys to values, like words to meanings: ages["Ann"] = 12. Looking up a key is fast, however big it is.

.get(key, 0) gives a default when the key isn't there; looping over a dictionary gives its keys, .items() gives keys and values together.

counts = {}
for word in input().split():
    counts[word] = counts.get(word, 0) + 1
for word, n in counts.items():
    print(word, n)

Watch for: Reading a key that isn't there stops the program with a KeyError: check with in, or use .get().

Exercises

Word frequencyCount how often each word appears (ignore capital letters).Intermediate
Letter chartCount the letters in a line (ignore capitals, spaces and punctuation) and draw a barIntermediate
Phone bookRead a phone book, then answer questions about it.Intermediate
AnagramsTwo words are anagrams when they use exactly the same letters, like listen andIntermediate
Group by first letterGroup words by their first letter.Intermediate
Average per studentRead scores; a student can appear several times.Intermediate
Stock countA shop records deliveries (positive) and sales (negative).Intermediate
First unique letterFind the first character that appears only once in a word.Intermediate