Week 9
Functions

Weekly Summary

In these first few weeks we have been focusing on code that gets input information from a human user and presents the results of calculations (processing) back to that same human user. This is a good way to start, but humans are often not the main audience/user for our code. While there is often a human at the end of the process, much of the calculation done is intended for the computer - either as the end user, or as an intermediary in a longer process that will only eventually end up at a human.

When we are writing code this is really intended to be used by the computer, rather than the human, we typically replace the input() and print() functions with other forms of getting input and providing output. The first way we do that is through the use of functions.

Recall from our prior Scratch Unit that we defined functions as:

This week we will learn how to write functions not only as code run by the computer, but also to provide encapsulation, modularity, and code appropriate for general re-use.

 

Learning Outcomes

By the end of the week students should be able to:

  • Reading Code
    • Given an existing function, and a set of input parameters to that function, identify the output returned by the function.
  • Writing Code
    • Given a problem statement that includes the name of a function and the parameters required by that function, write the Python code/definition of the provided function such that it solves the problem by returning correct output values.
      • For now, functions will be limited to those using
        • Mathematical Operators
        • Boolean Operators
        • Conditional Expressions
  • Debugging Code
    • Given a problem statement and a non-working Python function that attempts to solve the problem, identify where the function is incorrect and explain how to fix it.

 

Learning Materials

Textbook Readings

 

Our Lessons - Defining Functions

 

Introducing CS50 Duck Debugger

  • VIDEO: Introducing the AI based Duck Debugger
  • Harvard has an AI enabled Rubber Duck Debugger that we will allow you to use in this class on everything EXCEPT the competency demos.
  • This video explains how to use the tool and why we are ok with you using it.

 

Additional Explanations (Podcasts)

These videos add to the previous formal lessons. They are here as extra explanation on certain topics.

 

Practice Materials

Parsons Problems

These problems present the complete code for a program, but in a mixed-up order. Your task is to arrange the pieces correctly to "write" the described program. These problems are a great first step in learning because they allow you to focus on the semantics of programming rather than the syntax.

"Solutions" for these four programs are included in the Code Walkthrough section below.

We will have you look at some additional ones from this section next week.

 

Debugging Problems

Fixing programs that are "almost" correct but not yet functional is a crucial skill. As teachers, we often assume students will develop this skill by debugging their own work. However, it can be beneficial to provide explicit practice in debugging. The following problem is designed to give you semi-guided practice in debugging.

  1. Corn in an Elevator

The solution for this program is included in the Code Walkthrough section below.

 

(Paired) Practice Programs

Each week, I will provide you with several practice programs (non-graded) that I encourage you to attempt, with your partner, before tackling the graded assignments.

 

Code Walkthroughs

The following are videos and code solutions explaining the problems above, including the Parsons Problems, Debugging Problems, and (Paired) Programming Activity. You SHOULD NOT view these until you have either solved the activities yourself and want to see how I would do it, or you have tried at least twice and are still stumped.

Don’t jump to the "correct answer" too quickly. It’s beneficial to struggle with a problem for a day or two. We improve when we meet and overcome resistance. Learning comes from practice, so make sure to TRY before jumping to the solutions.

 

 

Graded Materials

The following programs are formally graded as part of the Unit 2 “Problem Set.” You should work on these individually. While working on these problems, you may refer to your notes, textbook, any programs you wrote, and my videos. However, you should significantly restrict your discussions with classmates. It is moderately acceptable to discuss how you solved a problem in general terms, but you should never show your code to a classmate, whether you are the one struggling or the one helping. You can talk about ideas, but not specific solutions.

Don't forget about the concept of Rubber Duck Debugging and the Rubber Duck AI from CS50. If you are getting stuck this week you should absolutely pull out your rubber duck and talk to it. If that isn't working, jump to Rubber Duck AI. Both are ok on your practice/homework (even the graded materials) although both will be off limits during your CD in two weeks.