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

• Do Now
• Lab - Magic 8-Ball
• Associated Reading - section 3.1 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
   • 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 Blocks vs Functions
     • Ask students to recall how they built custom blocks in Snap!
     • 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.
       • In SNAP! functions are blocks
       • 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
       • 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.
       • Random in Snap
     • Remind students what they saw in the Do Now - how to get a random integer: randint(0, 10).
       • Identify the 0 and 10 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.
   • Contract
     • Functions have a contract: you write down the arguments, their type, and the return type expected.
       • Ask students what the contract of randint is.
         • 2 values, of type integer, with an integer returned
       • 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

   • Check student progress and completion of the lab, wrap up by taking any final questions.

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.