Lesson 6.01: Introduction to Dictionaries

Learning Objectives

Students will be able to...

• Define and identify: dictionary, key, value
• Create dictionaries of key-value pairs
• Access and update items from dictionaries

Materials/Preparation

• Do Now
• Lab - Dictionaries & Memes
• Associated Reading - section 5.1 of Book
• Read through the do now, lesson, and lab so that you are familiar with the requirements and can assist students

Pacing Guide

Instructor's Notes

1. Do Now
   • Display the Do Now on the board.
   • Students will copy and edit code involving creating a dictionary and accessing items from that dictionary.

2. Lesson

   • Ask the students what type they think my_dictionary is.
     • Did anyone run the type() function to find out?
     • my_dictionary is a dictionary or a collection of key-value pairs. You use the key to look up the value in the dictionary.
       • Ask: what are the keys in the example from the Do Now? What are the associated values?
     • Keys and values can be of any type. The syntax is: {key : value, key : value, ...}
   • Ask the students what my_dictionary['dog'] did, and if this syntax reminds them of anything (lists!).
     • To get the value associated with a key in a dictionary you use square brackets.
     • You can also use my_dictionary.get(), which will return None if the key isn't there.
       • Note: You can pass in a second argument to get which takes the place of the None default.
   • Ask how students would get the value for chair or car.

   • Discuss what happened when students ran my_dictionary['kittens']?

     • Explain that this error is common and means that there is no value in the dictionary. To avoid this error, use the in keyword with an if statement. If a certain key is in a specified dictionary, it will return true. Otherwise it will return false.

       • Example:

         my_dictionary = {'a': 1, 'b': 2, 'c': 3}
         
         if 'a' in my_dictionary:
           print("It's there!")
         else:
           print("It's missing!")
         

3. Lab
   • Students will create a dictionary translating common internet phrases into their meanings.
4. Debrief
   • Review what was covered in today's lesson and check for understanding of the three concepts covered: dictionaries, keys, and values.

Accommodation/Differentiation

If any students are struggling with today's lesson, be prepared to offer additional examples of the usefulness of having key-value pairs.

Students that are moving quickly through the lab should work on the bonus and research how to add new key/value pairs to a dictionary.