Python For Kids For Dummies

Introduction

Hi! Welcome to the book. You’re going on a tour of all things Python. If you join me and code along with the projects, you’ll have your basic Python programming wings by the end of the book.

Everything in this book you need to know by doing — typing in the code or, better yet, thinking up the code before reading what I’ve done.

About This Book

This book walks you through all the parts you have to know about Python programming. You get examples. I talk about planning programs. And I help link you with the broader Python community so that you can head out there after mastering the projects in this book.

Conventions Used

Keep these things in mind while you read:

Sometimes words are in italics and then I explain the words. Here is an example: "The objects in the list are called elements." When you see this sentence, you know to keep your eyes peeled for a definition. (Elements are the objects in a list.)

Python code is written in a different font from the other text. Sometimes it’s inline with the text and looks like this: print('Hello World!').

Sometimes it’s a separate block of text, like this:

print('Hello World!')

Some code blocks have a >>> at the front of some lines. I’m showing you what happens when you’re using an interactive Python prompt. You need to type the code that follows the >>> in this book into the Python console that’s running on your computer to see what happens:

>>> my_message = Hello World!

>>> print(my_message)

The number of spaces at the front of each line of code is important. The length of your lines isn’t (technically) significant, but Python style guidelines suggest lines with no more than 79 characters (letters, numbers, spaces, or punctuation marks). This book isn’t as wide as your screen; it only lets me show 69 characters in a line. I’ve broken (split) some lines of code in the book. I split them to make sure that the code works and prints the right way. Be careful when you type them in! It’s not always clear how many spaces are at the front of the broken line.

I split lines two ways.

The first is implicitly. Basically, you can split the code in between any pair of parentheses at a comma. Python still sees it as a single line. The second and later parts of a split line should be indented to where the parentheses opened. Here’s an example from the code in Project 9:

values = (e.first_name, e.family_name,

          e.date_of_birth, e.email_address)

Even though you type this as two separate lines, Python sees it as a single line. (Think of it as one long line.) Type this code as you see it, pressing Enter at the end of each line and typing spaces at the start of each line so that the first character in the line is in the right place.

The second way to split a line is explicitly with the backslash character: \ (not /). Here’s an example from Project 9:

raw_input_prompt = Press: 1 for training,+\

2 for testing, 3 to quit.\n

You type these as two separate lines, with the \ at the end of the first line. However, Python sees it as a single line.

When using the Python interpreter in Projects 2 and 3 only, each new line starts with either … or >>>. If you don’t see these in the code in the book, then the previous line is meant to be typed in as one long line. For example, the following code is from Project 2:

>>> my_second_message = 'This name is a little long. Ideally, try to keep the name short, but not too short.'

This code doesn’t have … or >>> at the start of the second or third line. This means you’re supposed to type it all in before pressing Enter. Only press Enter after typing too short.' at the end, not after typing little long. and but not.

Sometimes the output on your computer may look a little different from what you see in this book. For example, when you run a program in later projects, you might see a restart line. On my screen, all the following text is on a single line:

>>> ================================ RESTART ================================

In Project 4 you see how to automatically indent your code. Until then, each time you need to indent code, do it by pressing the spacebar four times before you add your code. If you have to indent code two levels, press the spacebar eight times (that’s two levels of indent by four spaces per level) before typing your code, and so on. You need to do this for each line of the indented code.

When I’m explaining how code works, I often provide a code template — an outline of how to use the code. A sample template is: help([object name]). In this template, the keyword is help, and it needs to be followed by a pair of parentheses. The square brackets indicate something which is optional. The italics mean you need to fill in. Everything not in italics, type it just like it looks. Using this template, the code help(help) works (it gets help on the help keyword), and so does help(), with nothing inside the parentheses (since [object name] was optional).

Web addresses (URLs) and programming code are in monofont. If you’re reading this book on a device connected to the Internet, you can click the address to visit that website. Try it: www.dummies.com.

Sometimes you need to choose something from a menu. I’m not talking about a burger and fries. I mean actions. For example, I might ask you to choose File ⇒ New File. This means that you go to the File menu and choose New File from it.

The word Ctrl means the Ctrl key on your keyboard. Ctrl+A means that you press the key marked Ctrl while you press the A key. All at the same time. Then release both keys. If you’re using a Mac, your keyboard has a control key — use it. Ctrl-A means press the control key down and press the A key. Then release both keys. Don’t use the option or command keys.

If you’re using a Mac, assume that when I say Enter key, it means the Return key on your keyboard.

Foolish Assumptions

I’ve tried not to make too many assumptions about you in this book. In order to use this book, you need to be able to turn on your computer and navigate the Start Menu (on Windows). To install Python you will need administrator access for the computer you’re installing it on.

Learning anything is slow going to start. You are going to need a bit of determination to make it through the book. Hang in there.

Icons Used in This Book

warning The Warning icon tells you to watch out! This information may save you headaches. In some cases, you could lose data if you don’t heed the warnings.

remember You’re gonna use this information for a long, long time. Commit it to long-term gray matter.

tip The Tip icon marks shortcuts that make programming easier.

codeconnection Coding Connections icons mark information that applies not just to Python, but to coding in general.

Beyond the Book

You can find a bunch more information outside this book. Check out:

Cheat Sheet: This book has an online cheat sheet at www.dummies.com/cheatsheet/pythonforkids. The Cheat Sheet has a list of Python keywords, common built-ins, and selected functions from the standard library. Use it as a quick reference when you’re coding.

Dummies.com online articles and bonus projects: In addition to the projects in this book, there are some bonus projects online. You can get them from www.dummies.com/extras/pythonforkids.

python4kids.brendanscott.com: Visit my Python for Kids blog. Many of the projects in this book started out there. The blog has a dedicated blog entry for each of the projects and has a heap of other things you can try, too. If you’ve got feedback, you can leave it on the blog page that applies.

Where to Go from Here

Right now you should go to Project 1 to read more about what this language can do and to install it. Before you move on to Project 2, make sure you know about Ctrl+C. Then you’re ready to write your first Python program! Move in and out of the projects as you like. The code in each project stands on its own. Be careful though — even though they don’t use code from earlier projects, they often use concepts introduced earlier.

Week 1

Slithering into Python

This week you’re …

checkbox.png Getting Started with Python

checkbox.png Building Hello World!

PROJECT 1

Getting Started with Python

In this project, you’re introduced to Python: where it’s used and what it’s used for. I explain the two current versions of Python. This book is focused on Python 2.7 and I explain why. With my help during this chapter, you install a copy of Python 2.7 (if you don’t already have it installed) and fire it up. I also tell you how to stop once you’ve started.

This project also shows you how to get Python’s documentation, both built in to Python and online. I give you ways to search online for answers to your Python problems, just in case you’ve never searched the Internet before. You also read about the Python community, which is one place you can go for help or new ideas. All that, but no actual programming? No worries. Actual programming starts in Project 2.

TL;DR: If you’ve already installed Python, and you can start and stop it, then skip to Project 2.

Python and Why It’s Wonderful

Python is a programming language written by a person called Guido van Rossum in the 1990s. Programming languages allow you to control what a computer does and the way it does it.

Some of the things that make Python totes awesome (also known as really helpful and lots of fun) are:

Python code is easy to read and understand. In fact, I think Python’s code is sublime and beautiful. (Hey, that’s just my opinion.) Its beauty means you don’t even notice the way Python makes complex things simple. This makes Python easy to learn, which makes it perfect for kids.

Python is productive. It makes tough tasks simple. Almost any programming task is easier with Python than it is with other programming languages. Computer types call this RAD (for Rapid Application Development).

Python is dangerous. It has a lot of power. But with great power comes great responsibility. (Remember Spider-Man?) And you’ll have to use your powers for good, not evil. (If you want to use them for evil, you have to stop reading now.)

Python is a scripting language. The programs are fed into Python’s interpreter, which runs them directly, so there’s no compiling (which is the case for some other languages). It is faster and easier to get feedback on your Python code (finding errors, for example). Python means you complete and execute (run) your programs faster and that makes programming fun!

Python is cross platform. Almost anyone can use it, no matter what computer operating system they have. You can run pretty much any Python program on Windows, Mac, and Linux personal computers and from large servers through to tiny computers like the Raspberry Pi. (A Pi-specific project is waiting at dummies.com/go/pythonforkids for you.) You can even run Python programs on Android and iOS tablets. I even used my Android tablet to code some of the early projects in this book.

Python uses dynamic typing for its variables. This may not mean much to you if you’ve never done programming before. Dynamically typed variables make programming easier because they let you just start using a variable, rather than first explaining to the computer what the variable is supposed to be.

Python gets lots of help from third-party modules. This means that a lot of other people (third parties) have written libraries. A library is a bunch of code for doing something specific. This makes your work easier because you don’t have to start from scratch every time you write a new program; sometimes you can use the libraries already written. The Minecraft project online uses a third-party library to change a Minecraft game on a Raspberry Pi.

Python is free software. This means that the license terms for Python respect your freedom. I think this is pretty important. You can download and run Python without paying any money, and any program that you write with it is yours to use and share any way you want. It also means that the Python source code (the human-readable form of what the computer runs) is available so, when you’re feeling brave enough, you can look at how the Python developers wrote their code. (It’s written in a different programming language, though, d’oh!)

Pythons aren’t just snakes

The Python programming language is named after a comedy group called Monty Python, not the reptile. Monty Python was active mainly in the 1970s. (40 years ago! Forever and ever, right?) They had a British television show called Monty Python’s Flying Circus and have made lots of movies, the most notable of which is Monty Python and the Holy Grail.

Who’s Using Python

Python is used just about everywhere.

In space: The International Space Station’s Robonaut 2 robot uses Python for its central command system. Python is planned for use in a European mission to Mars in 2020 to collect soil samples.

In particle physics laboratories: Python helps understand the data analysis from some atom smashing experiments at the CERN Large Hadron Collider.

In astronomy: The MeerKat Radio telescope array (the largest radio telescope in the Southern Hemisphere) uses Python for its control and monitoring systems.

In movie studios: Industrial Light and Magic (Star Wars geniuses) uses Python to automate its movie production processes. Side Effects Software’s computer-generated imagery program Houdini uses Python for its programming interface and to script the engine.

In games: Activision uses Python for building games, testing, and analyzing stuff. They even use Python to find people cheating by boosting each other.

In the music industry: Spotify music streaming service uses Python to send you music.

In the video industry: Netflix uses Python to make sure movies play (stream) without stopping. Python is used a lot for YouTube.

In Internet search: Google used Python all over in its early development phase.

In medicine: The Nodality company uses Python to handle information that they use to search for a cure to cancer.

In your OS (admin-ing your datas): Operating systems like Linux and Mac OSX use Python for some of their administrative functions.

In your doorbell: Rupa Dachere and Akkana Peck say that you can automate your home with Python, hooking up sensors to your house. With it you can, for example, open and close the curtains or automatically turn on lights when you come in the room.

I could go on. The point is that Python will apply to whatever you’re interested in, no matter what it is.

Making Things with Python

You do these things while you work through this book:

Make a math trainer for practicing your times tables.

Make a simple encryption (a secret code) program.

Use Python on a Raspberry Pi to work with and modify your Minecraft world. (See www.dummies.com/go/pythonforkids for that project.)

When you’ve honed your mad skills and are ready to move on, there’ll be other things you can do:

Using Tkinter (or other widget sets), you can write user applications that use graphics rather than just text to interact with the user.

You can extend other programs like Blender (a 3D modeling program), GIMP (a 2D photo-retouching program), and LibreOffice (office programs), among many others by writing custom scripts. I had to fix some 3D models I was making in Blender. It would’ve taken forever to do by hand, so I wrote a Python script to do it quickly.

You can write games with graphics using Tkinter or the Pygame or Kivy libraries. The games in this book are text only.

You can use the matplotlib library to draw complex graphs for your math or science courses.

Using the openCV library, you can experiment with computer vision. People who are into robotics use it to help their robots see and grab things and to avoid obstacles when moving.

Whatever you want it to do, there’s a good chance someone has already written code to do it or to help you do it yourself.

Understanding This Book’s Pedagogical Approach

That title is just to impress your parents. (I hope they’re not reading this part. But look: If they don’t see that title, tell them that this book has a pedagogical approach — ped-uh-goj-i-cul. It means education or teaching.)

The point of this book is to give you a chunk of information about the programming concepts that you need to program in Python. The book is for you — a kid who can learn Python.

I am thorough

Thorough, yes. Will I include everything? No way. Many aspects of Python have lots of options. If I took you through all the possibilities of each option, you’d fall asleep (or throw this book out the window). If you do either of those things, then you won’t be learning.

As you read, remember that I’ve tried to introduce you to enough information so you can be a Python programmer, but not so much that you’d need superhuman powers to get through it. Expand on your own using the documentation and help.

You start pretty slowly with core (main) principles. If you think things aren’t going fast enough, skip ahead! The