• Due: Friday, June 5th no later than 5pm.
  • Submission instructions: complete the assigned number of activities in each of the assigned subsections of Chapter 12. You do not need to submit anything to Brightspace.
  • Deadline reminder: once this deadline passes, Runestone Interactive will no longer allow you to collect points for completing the activities.

Key ideas

  • A dictionary is an unordered collection of key-value pairs.
  • Creating an empty dictionary: homeruns = {}
  • Adding a key-value pair: homeruns["Babe Ruth"] = 713 (note: he hit 714)
  • Adding another pair: homeruns["Mickey Mantle"] = 536
  • Deleting an item: del homeruns["Mickey Mantle"]
  • Modifying an item: homeruns["Babe Ruth"] = 714
  • Determining the number of items in a dictionary: len(homeruns)


  • To retrieve all keys in a dictionary named inventory: inventory.keys()
  • To retrieve all keys as a list: list(inventory.keys())
  • To retrieve keys one at a time: for key in inventory:
  • To check if a key named “kiwi” exists: if "kiwi" in inventory


  • To retrieve all values: inventory.values()
  • To retrieve a specific value, producing a runtime error if the key is not present: inventory[key-name]
  • To retrieve a specific value, producing NO runtime error if the key is not present: inventory.get(key-name) or inventory.get(key-name, value-to-return-if-key-not-present)

Key-Value Pairs

  • To retrieve all key-value pairs: inventory.items()

Aliasing vs. copying

  • An example of an alias: dictionary1 = dictionary2
  • The expression dictionary2 is dictionary1 returns True
  • An example of a copy: dictionary2 = dictionary1.copy()
  • The expression dictionary2 is dictionary1 returns False
  • A dictionary handles sparse data well. For example, consider keeping track of how many times a word occurs in a novel such as The Catcher in the Rye. Only words that appear one or more times need to be stored.


  • Complete the required number of activities for each subsection in Dictionaries.

Grading - 10 points

  • 10 points - the required number of activities were completed for each subsection before the deadline.

Grading turnaround

This reading assignment will be graded with scores in Brightspace by office hours the following class day.

Optional activities

Activity 1

Download raven.py and raven.txt. Edit raven.py to find the counts of every letter in the text using a dictionary.

Activity 2

Download raven_words.py and

  1. Modify raven_words.py to produce a file word_counts.txt that contains the counts of each word in the file raven.txt, in alphabetical order. The first few lines of word_counts.txt should look something like this:
    a 15
    above 7
    adore 1
    again 1
    agreeing 1
    ah 2
    aidenn 1
    air 1
    all 4
    an 2
    ancient 1
    and 38
    angels 4
    answer 1

    Hint: you may need to cast a dict_keys object to a list using list()

  2. Modify your program to also print the longest word in the file.