Just For Fun 05: Function Calls in Code

Understanding Functions, Flow, and Mathematical Reasoning

Author

OBC

Published

August 30, 2025

Lesson Objectives

By the end of this lesson, you will be able to:

Identify and describe the anatomy of a Python function
Explain the flow of execution in a Python script
Discuss the mathematical reasoning behind calculating the area of a square
Experiment with function calls and inputs interactively

Introduction

In this lesson, you’ll explore the structure of Python code, focusing on how functions are defined and called. We’ll use a simple example that calculates the area of a square to illustrate key concepts.

Key Concepts

💡 Concept 1: Function Definition & Calls

A function in Python is a reusable block of code that performs a specific task. Functions are defined using the def keyword, followed by the function name and parameters. To use a function, you “call” it by its name and provide the required arguments.

Example:

def squareArea(s: float) -> float:
    """ determine area of square"""
    return s * s

💡 Concept 2: Flow of Execution

Python executes code from top to bottom. The main() function is often used as a “driver” to organize the flow. When main() is called, it runs the code inside it, including any function calls.

Example:

def main() -> None:
    sideLength = 5
    print(f"Length {sideLength}")
    print(f" Area: {squareArea(sideLength)}")

Example 1a: Calculating the Area of a Rectangle

What this code does: Defines a function to calculate the area of a rectangle and calls it with sample values.

Example Code:

def rectangleArea(length: float, width: float) -> float:
    """ determine area of rectangle"""
    return length * width

print(rectangleArea(6, 3))

Loading Python interpreter…

Example 1b: Calculating the Area of a Circle

What this code does: Defines a function to calculate the area of a circle and calls it with a sample value.

Example Code:

import math
def circleArea(radius: float) -> float:
    """ determine area of circle"""
    return math.pi * radius * radius

print(circleArea(2))

Loading Python interpreter…

Example 1c: Calculating the Volume of a Cube

What this code does: Defines a function to calculate the volume of a cube and calls it with a sample value.

Example Code:

def cubeVolume(s: float) -> float:
    """ determine volume of cube"""
    return s ** 3

print(cubeVolume(3))

Loading Python interpreter…

Challenge Questions

Choose a function to check whether a side can have a negative distance value. What should the function do if it receives a negative value?
Change the one of the circleArea or cubeVolume functions to handle a radius of zero or negative values. Should the area be zero or should it raise an error?
Challenge: Write a function to calculate the volume of a cylinder (π * r^2 * h). Try different values for radius and height.
Challenge: Write a function to calculate the area of a triangle given its base and height. Test your function with different values.

Use the interactive code fields above to modify and run your solutions. Have fun experimenting and solving these challenges!

Your Turn!

Challenge Tasks:

Try using different types of inputs (integers, floats, strings, booleans, complex numbers) and observe the results.
Modify the function to handle invalid inputs gracefully (e.g., using type checking or error handling).
Add comments to explain each part of the code.
Write your own function to calculate the area of a rectangle.

Use any of the terminals above to experiment with these challenges!

Summary

What You Learned

In this lesson, you explored: - The structure and anatomy of Python functions - How function calls work and how data flows through a program - Mathematical reasoning for calculating area - How different input types affect function behavior

Key Takeaways

Functions are reusable blocks of code
Flow of execution is organized using functions like main()
Mathematical formulas can be implemented directly in code
Input types matter for function behavior

Additional Resources