lesson.md

Lesson 3.01: Built-In Functions

Learning Objectives

Students will be able to...

• Define and identify: function, arguments, calling, importing, returning.
• Call the built-in randint function, using arguments.
• Utilize code other people have written in the Python documentation.
• Understand the difference between printing and returning.

Materials/Preparation

• 3.01 Slide Deck
• Do Now
• Lab - Magic 8-Ball (docx) (pdf)
• Associated Reading
• Read through the do now, lesson, and lab so that you are familiar with the requirements and can assist students.

Pacing Guide

Duration	Description
5 Minutes	Do Now
10 Minutes	Lesson
35 Minutes	Lab
5 Minutes	Debrief

Instructor's Notes

1. Do Now

• Give students 3-4 minutes to follow the instructions on the Do Now page.
• Debrief the answers to the questions on the Do Now by calling on students to respond.

2. Lesson

Build Your Own Functions

• Function: a named sequence of statements. You can use functions to perform complex calculations, graphical operations, and various other purposes. When you define a function, you specify the name and the sequence of statements. Later, you can "call" the function by name.

Function Contract

A function definition is like a contract: you tell the programmer what elements the function expects (name and type of arguments) and the function will perform its purpose. It is good practice to use a comment to specify the purpose and contract of a function, including the type of value it returns, if it returns a value.

    # Name:
    # Purpose:
    # Arguments:
    # Returns:

• Explain that we have already gotten used to calling functions like type() and print().
• Ask students how they would create a random number generator.
• Sounds hard! Luckily someone has already done that: the random library (essentially a bunch of code written by someone else) which has many associated functions.

Back to the Do Now

• Remind students what they saw in the Do Now - how to get a random integer: randint(0, 3).
• Identify the 0 and 3 in this example as arguments, or values passed into the function.
• Ask students what the argument is when we use print or type.
• randint gives back a value that you might want to store - this is called returning. If nothing is given back, the return value is None.

More on Function Contracts

• Functions have a contract: you write down the name, purpose, arguments with their type, and the return type expected.
• Ask students what the contract of randint is.

    # Name: randint
    # Purpose: generate a pseudo-random integer N such that a <= N <= b
    # Arguments: 2 values of type integer: a and b
    # Returns: integer

• Since randint is written by someone else there is a place where that contract is written out - Documentation. Have students begin the lab, which will instruct them to find the Python documentation for the random library.

3. Lab

• Students look through random library documentation, practice importing different random functions and using them.
• Create a Magic 8-Ball program using a list and randint.

4. Debrief/Exit Ticket

• In their notebooks, have students write down 2 things they learned today to reinforce learning.

Accommodation/Differentiation

If students are moving quickly, find another library to import from (see bonus in the lab) OR allow students to move on to creating their own functions.