Lesson 3.04: Debuging and Scope

Learning Objectives

Students will be able to...

• Define and identify: scope, aliasing, stack trace
• Understand that changing a list in a function updates the list outside of the function
• Understand that updating variables in a function does not affect the variable outside of the function
• Understand global variables
• Draw a simple stack trace

Materials/Preparation

• Do Now
• Lab - Aliasing & Scope
• Associated Reading - section 3.4 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
   • Students have a chance to think about what & discuss what concepts they have been most challenged by.
   • Next, students practice passing a list as an argument and updating that list within the function.
2. Lesson
   • Discuss what students observed in the Do Now and take time, if needed, to go over questions about concepts that students find challenging.
   • Explain the concept of aliasing. You can draw on the board a diagram of the variable pointing to a list. Note that when passing the location of a list you are not passing the actual value, so the list can be changed.
   • Scope of functions
     • Explain to students that variables in functions are the arguments and the ones you define in the function. To use variables from outside the function you must put the phrase global name_of_variable.
     • Global variables: variables used in many different functions.
     • NOTE: We use the 'ALL CAPS' convention for global variables
       • Discuss that programming languages frequently have conventions like camelCase for function names, ALL_CAPS for globals, and underscore_separated for variables. It helps make code more readable, but isn't essential to functionality (in most cases)
         • Demonstrate how to draw the Stack Diagrams shown in the course book (found in section 3.4) and explain how they show the scope of variables as they related to functions.
         • Point out the error messages that will occur if you use a variable out of it's scope.
   • Debugging
     • Help students follow their program to understand how the code is working
     • Explain how the use of print statements throughout your code can let you know where in the program things are not operating as expected.

3. Lab

   • This lab has students running code that gets them thinking about aliasing and scope. They must also create a stack trace for a program to show their understanding of scope.

4. Debrief

   • Take time to review the concepts covered today: scope, aliasing, and stack traces.
   • Call a few students to the board to draw their stack traces from the lab and talk through them.

Accommodation/Differentiation

If students are moving quickly, they can look ahead at the project spec or research the game Oregon Trail for context.