INTRODUCTION
Welcome to Python Playground! Within these pages, you’ll find 14 exciting projects designed to encourage you to explore the world of programming with Python. The projects cover a wide range of topics, such as drawing Spirograph-like patterns, creating ASCII art, 3D rendering, and projecting laser patterns in sync with music. In addition to being fun in and of themselves, these projects are designed to be jumping-off points for you to explore your own ideas by expanding on each of the projects.
Who Is This Book For?
Python Playground is written for anyone curious about how to use programming to understand and explore ideas. The projects in this book assume that you know basic Python syntax and basic programming concepts and that you’re familiar with high-school level mathematics. I’ve done my best to explain in detail the math you need for all projects.
This book is not intended to be your first book on Python. I won’t walk you through the basics. I will, however, show you how to use Python to solve a variety of real-world problems in a series of nontrivial projects. As you work through the projects, you’ll explore the nuances of the Python programming language and learn how to work with some popular Python libraries. But perhaps even more importantly, you’ll learn how to break down a problem into parts, develop an algorithm to solve that problem, and then implement a solution from the ground up using Python. It can be difficult to solve real-world problems because they are often open-ended and require expertise in various domains. But Python offers the tools to facilitate problemsolving. Overcoming difficulties and finding solutions to real problems is the most important part of your journey on the way to becoming an expert programmer.
What’s in This Book?
Let’s take a quick tour through the chapters in this book.
Part I: Warming Up
Chapter 1 will show you how to parse iTunes playlist files and gather useful information from them, such as track lengths and common tracks. In Chapter 2, we use parametric equations and Turtle graphics to draw curves like the ones generated by a Spirograph.
Part II: Simulating Life
This part is about using mathematical models to simulate phenomena. In Chapter 3, you’ll learn how to implement the Conway’s Game of Life algorithm to generate dynamic patterns that create other patterns as a sort of simulation of artificial life. Chapter 4 will show you how to create realistic plucked string sounds using the Karplus-Strong algorithm. Then, in Chapter 5, you’ll learn how to implement the Boids algorithm to simulate the flocking behavior of birds.
Part III: Fun with Images
This part will introduce you to reading and manipulating 2D images with Python. Chapter 6 shows you how to create ASCII art from an image. In Chapter 7, you’ll make a photomosaic, and in Chapter 8, you’ll learn how to generate autostereograms, which create the illusion of a 3D image.
Part IV: Enter 3D
The projects in this part use the OpenGL 3D graphics library. Chapter 9 introduces the basics of using OpenGL to create simple 3D graphics. In Chapter 10, you’ll create a particle simulation—a fountain of fireworks that uses math and OpenGL shaders for computation and rendering. Then in Chapter 11, you’ll use OpenGL shaders to implement a volume ray casting algorithm to render volumetric data—a technique commonly used for medical imaging such as MRI and CT scans.
Part V: Hardware Hacking
In the final part, you’ll use Python to explore the Arduino microcontroller and the Raspberry Pi. In Chapter 12, you’ll use the Arduino to read and plot sensor data from a simple circuit. In Chapter 13, you’ll combine Python with an Arduino to control two rotating mirrors and a laser to produce a laser show that responds to sound. In Chapter 14, you’ll use the Raspberry Pi to build a web-based weather monitoring system.
Why Python?
Python is an ideal language for exploring programming. As a multiparadigm language, it provides you with a lot of flexibility in how you structure your programs. You can use Python as a scripting language to simply execute code, as a procedural language to organize your program into a collection of functions which call each other, or as an object-oriented language that uses classes, inheritance, and modules to build up a hierarchy. This flexibility allows you to choose the programming style most suited to a particular project.
When you develop using a more traditional language like C or C++, you have to compile and link your code before you can run it. With Python, you can run it directly after editing. (Under the hood, Python compiles your code into an intermediate bytecode that is then run by the Python interpreter, but these processes are transparent to you, the user.) In practice, the process of modifying and running your code over and over is much less cumbersome with Python.
Furthermore, the Python interpreter is a very handy tool for checking code syntax, getting help with modules, doing quick computations, and even testing code under development. For example, when I write Python code, I keep three windows open: a text editor, a shell, and a Python interpreter. As I develop code in the editor, I import my functions or classes into the interpreter and test them as I go.
Python has a very small set of simple and powerful data structures. If you already understand strings, lists, tuples, dictionaries, list comprehensions, and basic control structures such as for and while loops, you’re off to a great start. Python’s succinct and expressive syntax makes it easy to do complex operations with just a few lines of code. And once you’re familiar with Python’s built-in and third-party modules, you’ll have an arsenal of tools to tackle real problems like the ones covered on this book. There are standard ways to call C/C++ code from Python and vice versa, and because you can find libraries to do almost anything in Python, it’s easy to combine Python with other language modules in bigger projects. This is why Python is considered a great glue language—it makes it easy to combine diverse software components. The hardware projects at the end of this book demonstrate how Python can work side by side with Arduino code and JavaScript. Real software projects often use a mix of software technologies, and Python fits very well into such layered architectures.
The following example demonstrates the ease of working with Python. While developing code for the Raspberry Pi weather monitor in Chapter 14, I wrote this string looking at the oscilloscope output from the temperature/humidity sensor:
0011011100000000000110100000000001010001
Since I don’t speak binary (especially at 7 AM on a Sunday morning), I fired up the Python interpreter and entered:
>>> str = '0011011100000000000110100000000001010001'
>>> len(str)
40
>>> [int(str[i:i+8], 2) for i in range(0, 40, 8)]
[55, 0, 26, 0, 81]
This code splits up the 40-bit string into five 8-bit integers, which I can actually interpret. The data above is decoded as a 55.0 percent humidity reading at a temperature of 26.0 degrees centigrade, and the checksum is 55 + 26 = 81.
This example demonstrates the practical use of the Python interpreter as a very power calculator. You don’t need to write a complete program to do quick computations; just open up the interpreter and get going. This is just one of the many reasons why I love Python, and why I think you will too.
Python Versions
This book was built with Python 3.3.3, but all code is compatible with Python 2.7.x and 3.x.
The Code in This Book
I’ve done my best throughout this book to walk you through the code for each project in detail, piece by piece. You can either enter the code yourself or download the complete source code (using the Download Zip option) for all programs in the book at https://github.com/electronut/pp/.
You’ll find several exciting projects in the following pages. I hope you have as much fun playing with them as I had creating them. And don’t forget to explore further with the exercises presented at the end of each project. I wish you many happy hours of programming with Python Playground!