Adventures in Python

Introduction

ARE YOU AN intrepid adventurer? Do you love trying new things and learning new skills? Would you like to bring your own ideas to life with technology? If the answer is a resounding Yes! then this is the book for you. Your adventures with Python start here! During your adventures you’ll learn a lot about programming with Python. You’ll create some really fun programs along the way, including games and animations.

Before you take your first step, take some time with this introduction to understand what you’ll be doing and answers some of the questions you might have.

What Is Programming?

First off, what is programming? Put simply, programming is giving the computer a set of instructions to do something you want. For example, when you play a computer game programs determine what the game will do when you press a button and what is displayed on the screen.

Just as programming is giving the computer a set of instructions, a program is a set of instructions that has been written by a programmer.

You write these instructions using a programming language. There are many different programming languages, which you can think of as similar to human languages like English or French. Each programming language has its own way of doing things but they all share the same fundamental concepts.

ImageD A program is a set of instructions that has been written by a programmer to instruct the computer to do something.

A programming language allows you to give instructions to a computer. With a programming language you can create programs that control what your computer does.

As a programmer, you have a lot of choice when choosing a programming language to use. So why choose Python? Well, Python is a good language to learn for beginners. It is designed so that it is relatively easy for humans to read. The layout and words it uses for its instructions make it easier to learn than other languages, such as Java or C++. Python is even used in the real world—in fact, it is one of the most popular programming languages used by professional programmers, who use it to do all sorts of things, from analysing scientific data to making games. You can see an example of some Python code in Figure I-1.

FIGURE I-1 The code of a program that generates a circular progress bar. You will learn how to create programs like this one in your adventures.

This introduction is intended to help you get set up with Python on your computer. It’s here to make sure you start your journey on the right foot and have everything you need to get going.

What Is Python and What Can You Do With It?

As I’ve mentioned, the Python programming language is an excellent programming language for beginners. Python is designed so that it is easy to read by people. The way that Python is laid out and the commands it uses all make it straightforward to read and understand.

You can do some amazing things with Python. Here are just some of the many things it is used for:

Making windows with buttons and text fields

Creating computer games

Making animations

Building websites

Analysing scientific data

Hacking computers

Who Should Read This Book?

Adventures in Python is for any young person who has an interest in making things happen on a computer. You might perhaps be unsure of how to get started or want to develop your current skills further. Whatever your reasons, this book will be your guide for a journey with Python. Your adventures will take you from installing Python, through learning the basics of programming, to discovering how to create your own project. By the end of your adventures you will have acquired the skills you need to create whatever you want!

What You Will Learn

With this book you will discover some of the amazing things you can do with Python. You’ll learn about the fundamental programming concepts needed to design and make your own programs.

The Python projects in this book are arranged in adventures. All the projects in an adventure are grouped by a similar topic. For example, in Adventure 7 you’ll create several programs that show you how to use the mouse with your Python programs.

The programming concepts you’ll learn include Python code that enables your programs to make decisions, allows your programs to repeat complex tasks in a short amount of time and a whole lot more. By building on top of these concepts in your adventures you’ll also develop graphical user interfaces, animations and games.

What You Will Need for the Projects

Python is a programming language that is cross-platform. This means that it can run on computers with different operating systems. For example, you can write a program on a computer that runs Windows 7 and it will also work on an Apple Mac. There are a couple of slight differences in the way that Python works on different operating systems, but you won’t come across these in this book, and they aren’t that common.

ImageD An operating system is software that allows your computer to do its basic functions, such as allowing you to use mice and keyboards on the computer, save files and connect to the Internet. Microsoft Windows and Mac OS X are two examples of operating systems.

A cross-platform programming language works on computers with different operating systems. This means you can write a program on one computer and it will work on most other computers.

Another benefit of Python being cross-platform is that you can use this book whether you use Windows, Mac or Linux—the programs will work just the same on all of them.

So, all you need for your adventures is a computer running Windows, Mac or Linux, an Internet connection, a mouse, keyboard and computer monitor. That’s it! You don’t need anything else.

ImageD Although it is possible to run Python on Android tablet computers, not all of the things covered in this book are available on a tablet. It’s not currently possible to complete most of the adventures with a tablet or phone.

How This Book Is Organised

This book contains Python programs that teach you the basics of the Python programming language and the different things it can do. As you’re led through some really fun and creative programs, you’ll learn how to use Python.

Adventure 1 introduces Python and shows you how to create programs that use text. You’ll create some cool programs, like a control panel for an imaginary spaceship. In Adventure 2, you’ll create drawings using Python’s built-in turtle module. You’ll make pictures and build on the things you learned about Python in Adventure 1.

Adventures 3 and 4 introduce you to making programs that use graphical interfaces that include familiar things like buttons, text boxes and sliders.

From the Adventure 5 onwards, you’ll be introduced to the PyGame library for Python. The PyGame library makes it easier to do a wide range of things with Python, including making computer games of your own. You’ll find instructions on how to install PyGame in the Appendix.

In Adventure 5, you’ll use some of PyGame’s features to draw shapes and make animations, and in Adventure 6 you’ll find out how to use PyGame to detect keyboard presses for input in your programs, allowing you to take control of what happens when the program runs. In Adventure 7, you’ll learn how to use the mouse with your programs.

Adventure 8 shows you how to use images in your PyGame program and guides you through a series of fun programs, including controlling a character to walk across the window using the keyboard. In Adventure 9, you’ll learn how to use sounds and music with PyGame so you can add music and sounds to your games.

Adventure 10 takes you on a final, big adventure in which you will combine many of the things you learned in your earlier adventures to create a game in which two players compete to collect coins. The game wraps up what you’ve learned–all in a single program. Through your adventures, you’ll learn a lot about programming.

Time to get going!

Setting Up Python

This section will show you how to set up Python on your computer. Choose the section that matches your operating system (OS) to get started.

Windows 8

Microsoft Windows 8 is an operating system that is widely used all over the world. At the time this book is being written, Windows 8 is the operating system that is on most new computers. If you’re using Windows 8 on your computer, follow these instructions to install Python.

Installing

Installing Python on Windows 8 is quite straightforward. Follow these steps to install it:

Open a web browser (such as Internet Explorer, Chrome or Firefox).

In the web browser, click in the address bar.

Type this text into the address bar: python.org/downloads.

Press the Enter key on the keyboard.

When the page loads, click on Download Python 2.7.8 (sometimes the file will download when you click this link, if it does skip Step 6).

Scroll down to the Download section and click on Windows x86 MSI Installer (see Figure I-2).

When the file has downloaded, open it.

When the installer window opens, select Install for all users and click next.

Click next again.

Click next a third time!

When asked if you want the program to install software on your computer, click Yes.

Wait for it to install.

Once it is installed, click Finish (see Figure I-3).

Python is now installed on your computer.

FIGURE I-2 Downloading Python for Windows 8

FIGURE I-3 Python has been installed on Windows 8.

Opening

Now that Python is installed, you can open it. IDLE is a program that allows you to run, make and edit Python programs. It includes lots of helpful features to make creating programs straightforward. Remember these steps to open Python with IDLE as you’ll need them throughout your adventures.

To open IDLE, follow these steps:

Press the Windows key on your keyboard.

Type IDLE and select the Idle (Python GUI) option. IDLE is one of the ways you can use Python on your computer, and the program has many features that help you when you write your programs.

IDLE will now open—you are ready to start using Python (see Figure I-4)! It’s time to try your first program, so skip to Creating Your First Program at the end of this chapter.

FIGURE I-4 IDLE installed and Python opened on Windows 8

Windows 7

Despite not being the most recent version of Windows, Microsoft Windows 7 is still very widely used. All the screenshots in this book were taken on Windows 7. If your computer uses Windows 7, here’s how to install Python.

Installing

Follow these step-by-step instructions to install Python on Windows 7:

Open a web browser (such as Internet Explorer, Chrome or Firefox).

In the address bar, type www.python.org/downloads to go to the Downloads page on the Python website.

Once the page has loaded, click on the button labeled Download Python 2.7.8 ( Figure I-5). Sometimes the file will download when you click this link, if it does skip Step 4.

Scroll down to the Download section and click on Windows x86 MSI Installer.

Wait for the file to download, then go to your Downloads folder and double-click on the python-2.7.8.msi file.

A dialog box might appear asking if you are sure you want to run the program. If this happens, click the Run button to continue.

The installer will ask you if you want to install Python for all users on the computer, or just the current user. Choose the option to Install For All Users, and click Next.

Click Next again . . . and again!

A dialog box will appear asking if you want to allow the file to make changes to your computer. Click Yes.

Python will now install on your computer. Wait until this finishes before doing anything else.

Once the installation completes (see Figure I-6), click Finish and follow the steps in the next section to open Python.

FIGURE I-5 Downloading Python for Windows 7

FIGURE I-6 Python has been installed on Windows 7.

Opening

IDLE is the name of a program that allows you to run, make and edit Python programs. It includes lots of helpful features to make creating programs straightforward. Remember these steps to open Python with IDLE as you’ll need them throughout your adventures:

You can open Python from the Start menu. Click the Start button in the bottom-left corner of the screen.

Click on All Programs to bring up the list of programs installed on your computer.

Select the Python 2.7 folder to show all the options for using Python. The list of programs should be in alphabetical order.

Click on the IDLE (Python GUI) icon in the start menu. IDLE is one of the ways you can use Python on your computer, and the program has many features that help you when you write your programs.

Wait for IDLE to open (see Figure 1-7). Congratulations! You are ready to start using Python! It’s time to try your first program, so skip to Creating Your First Program at the end of this chapter.

FIGURE I-7 IDLE installed and Python opened on Windows 7

Mac OS X

The operating system that comes with Apple Mac computers is Mac OS X. There are many different versions of this operating system, and any version of Mac OS X after and including 10.6 will work with these installation instructions. To install Python on your Mac, follow the instructions in this section.

Installing

Follow these steps to install Python on your computer:

Open a web browser (such as Safari, Chrome or Firefox).

In the address bar, type www.python.org/download and press the Enter key to go to the Download page for Python.

Click on the button that says Download Python 2.7.8 (sometimes the file will download when you click this link, if it does skip Step 4).

When the page has loaded, scroll down to find the Python 2.7.8 Mac OS X 64-bit/32-bit x86-64/i386 file. Click on it to download it (see Figure 1-8). Be a bit careful here—there are several versions of Python listed, so make sure you click on the one that that says Python 2.7.8 and Mac.

FIGURE I-8 Downloading Python for Mac OS X

ImageD Don’t download Python 3! There are two versions of Python that are commonly used, Python 2.7 and Python 3. Some of the software used in your adventures only support Python 2.7, so make sure you don't download Python 3.

When the file has downloaded, click on the Finder icon and go to your Downloads folder.

Find the file you just downloaded. It should be called python-2.7.8-macosx10.6.dmg.

Double-click on the file to open it.

Right-click on Python.mpkg and click on Open With⇒Installer (see Figure I-9).

FIGURE I-9 Installing Python on a Mac

When asked if you want to open it, click Open. Then click Continue three times and then click Agree.

Next, click Install and when prompted type in your password and click Install Software.

Wait while Python installs.

When the installation completes (see Figure I-10) you can now use Python on your computer. (It’s also a good idea to remove the installer that you no longer need.) Click Close.

FIGURE I-10 Python has been installed on the Mac

On the desktop, right-click on the Python 2.7.8 disk image and select Eject.

Opening

IDLE is the name of a program that allows you to run, make and edit Python programs. It includes lots of helpful features to make creating programs straightforward. These steps show you how to open IDLE. Remember these steps, as you will be using them throughout the book:

Open a new finder window and click on the Applications folder on the sidebar to show all the applications installed on your computer.

In the list of installed applications, find Python 2.7. Double-click on Python 2.7 to open the folder.

Double-click on IDLE. Wait until IDLE loads. IDLE is one of the ways you can use Python on your computer, and the program has many features that help you when you write your programs.

ImageD If you get a WARNING about Tcl/Tk being unstable, just ignore it.

When IDLE has loaded, you’re ready to start using Python (see Figure I-11)! It’s time to try your first program, so skip to Creating Your First Program at the end of this chapter.

FIGURE I-11 IDLE installed and Python opened on Mac

Linux (Ubuntu)

Operating systems that are based on Linux are free to install and use on your computer. There are many different distributions of Linux, each with its own unique flavour. For this set of instructions, I’ve chosen to show you how to install Python on the Ubuntu 14.04 distribution. These instructions should work on most other distributions, though you might find they don’t work on all of them.

Installing

Ubuntu 14.04 comes with Python 2.7 pre-installed. Despite this, you still need to install IDLE. IDLE is the name of a program that allows you to run, make and edit Python programs. It includes lots of helpful features to make creating programs straightforward. Follow these steps to install IDLE for Python 2.7:

Click on the Dash button, or press the super key, to open