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Head First Learn to Code by Eric Freeman

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Chapter 1. how to use this book: Intro


Who is this book for?

If you can answer “yes” to all of these:

  1. Do you want to learn, understand, and remember how to program?

  2. Do you prefer stimulating dinner party conversation to dry, dull, academic lectures?

this book is for you.

This is NOT a reference book. Head First Learn to Code is a book designed for learning to code. It’s not an encyclopedia of programming facts (you have Google for that, right?).


[Note from marketing: this book is for anyone with a credit card.]

Who should probably back away from this book?

If you can answer “yes” to any one of these:

  1. Are you completely new to computers?

    If you don’t know your way around your computer, how to manage files and folders, how to install apps, or how to use a word processor, you should probably learn those first.

  2. Are you a kick-butt programmer looking for a reference book?

  3. Are you afraid to try something different? Would you rather have a root canal than mix stripes with plaid? Do you believe that a technical book can’t be serious if we have fun learning to code?

this book is not for you.


We know what you’re thinking.

“How can this be a serious book?”

“What’s with all the graphics?”

“Can I actually learn it this way?”

And we know what your brain is thinking.

Your brain craves novelty. It’s always searching, scanning, waiting for something unusual. It was built that way, and it helps you stay alive.

Today, you’re less likely to be a tiger snack. But your brain’s still looking. You just never know.

So what does your brain do with all the routine, ordinary, normal things you encounter? Everything it can to stop them from interfering with the brain’s real job—recording things that matter. It doesn’t bother saving the boring things; they never make it past the “this is obviously not important” filter.

How does your brain know what’s important? Suppose you’re out for a day hike and a tiger jumps in front of you. What happens inside your head and body?

Neurons fire. Emotions crank up. Chemicals surge.

And that’s how your brain knows…


This must be important! Don’t forget it!

But imagine you’re at home, or in a library. It’s a safe, warm, tiger-free zone. You’re studying. Getting ready for an exam. Or trying to learn some tough technical topic your boss thinks will take a week, 10 days at the most.

Just one problem. Your brain’s trying to do you a big favor. It’s trying to make sure that this obviously non-important content doesn’t clutter up scarce resources. Resources that are better spent storing the really big things. Like tigers. Like the danger of fire. Like how you should never again snowboard in shorts.

And there’s no simple way to tell your brain, “Hey brain, thank you very much, but no matter how dull this book is, and how little I’m registering on the emotional Richter scale right now, I really do want you to keep this stuff around.”


Metacognition: thinking about thinking

If you really want to learn, and you want to learn more quickly and more deeply, pay attention to how you pay attention. Think about how you think. Learn how you learn.

Most of us did not take courses on metacognition or learning theory when we were growing up. We were expected to learn, but rarely taught how to learn.

But we assume that if you’re holding this book, you really want to learn how to code to create programs and apps. And you probably don’t want to spend a lot of time. And you want to remember what you read, and be able to apply it. And for that, you’ve got to understand it. To get the most from this book, or any book or learning experience, take responsibility for your brain.

The trick is to get your brain to see the new material you’re learning as Really Important. Crucial to your well-being. As important as a tiger. Otherwise, you’re in for a constant battle, with your brain doing its best to keep the new content from sticking.


So how DO you get your brain to think coding is as important as a tiger?

There’s the slow, tedious way, or the faster, more effective way. The slow way is about sheer repetition. You obviously know that you are able to learn and remember even the dullest of topics, if you keep pounding on the same thing. With enough repetition, your brain says, “This doesn’t feel important to him, but he keeps looking at the same thing over and over and over, so I suppose it must be.”

The faster way is to do anything that increases brain activity, especially different types of brain activity. The things on the previous page are a big part of the solution, and they’re all things that have been proven to help your brain work in your favor. For example, studies show that putting words within the pictures they describe (as opposed to somewhere else in the page, like a caption or in the body text) causes your brain to try to make sense of how the words and picture relate, and this causes more neurons to fire. More neurons firing = more chances for your brain to get that this is something worth paying attention to, and possibly recording.

A conversational style helps because people tend to pay more attention when they perceive that they’re in a conversation, since they’re expected to follow along and hold up their end. The amazing thing is, your brain doesn’t necessarily care that the “conversation” is between you and a book! On the other hand, if the writing style is formal and dry, your brain perceives it the same way you experience being lectured to while sitting in a roomful of passive attendees. No need to stay awake.

But pictures and conversational style are just the beginning.

Here’s what WE did:

We used pictures, because your brain is tuned for visuals, not text. As far as your brain’s concerned, a picture really is worth 1,024 words. And when text and pictures work together, we embedded the text in the pictures because your brain works more effectively when the text is within the thing the text refers to, as opposed to in a caption or buried in the text somewhere.


We used redundancy, saying the same thing in different ways and with different media types, and multiple senses, to increase the chance that the content gets coded into more than one area of your brain.

We used concepts and pictures in unexpected ways because your brain is tuned for novelty, and we used pictures and ideas with at least some emotional content, because your brain is tuned to pay attention to the biochemistry of emotions. That which causes you to feel something is more likely to be remembered, even if that feeling is nothing more than a little humor, surprise, or interest.

We used a personalized, conversational style, because your brain is tuned to pay more attention when it believes you’re in a conversation than if it thinks you’re passively listening to a presentation. Your brain does this even when you’re reading.


We included more than 120 activities, because your brain is tuned to learn and remember more when you do things than when you read about things. And we made the exercises challenging-yet-doable, because that’s what most people prefer.

We used multiple learning styles, because you might prefer step-by-step procedures, while someone else wants to understand the big picture first, while someone else just wants to see a code example. But regardless of your own learning preference, everyone benefits from seeing the same content represented in multiple ways.


We include content for both sides of your brain, because the more of your brain you engage, the more likely you are to learn and remember, and the longer you can stay focused. Since working one side of the brain often means giving the other side a chance to rest, you can be more productive at learning for a longer period of time.


And we included stories and exercises that present more than one point of view, because your brain is tuned to learn more deeply when it’s forced to make evaluations and judgments.

We included challenges, by providing exercises and by asking questions that don’t always have a straight answer, because your brain is tuned to learn and remember when it has to work at something. Think about it—you can’t get your body in shape just by watching people at the gym. But we did our best to make sure that when you’re working hard, it’s on the right things. That you’re not spending one extra dendrite processing a hard-to-understand example, or parsing difficult, jargon-laden, or overly terse text.

We used people. In stories, examples, pictures, and so on, because, well, you’re a person. And your brain pays more attention to people than it does to things.

We used an 80/20 approach. We assume that if you’re going to be a kick-butt programmer, this won’t be your only book. So we don’t talk about everything. Just the stuff you’ll actually need.


Here’s what YOU can do to bend your brain into submission

So, we did our part. The rest is up to you. These tips are a starting point; listen to your brain and figure out what works for you and what doesn’t. Try new things.

  1. Slow down. The more you understand, the less you have to memorize.

    Don’t just read. Stop and think. When the book asks you a question, don’t just skip to the answer. Imagine that someone really is asking the question. The more deeply you force your brain to think, the better chance you have of learning and remembering.

  2. Do the exercises. Write your own notes.

    We put them in, but if we did them for you, that would be like having someone else do your workouts for you. And don’t just look at the exercises. Use a pencil. There’s plenty of evidence that physical activity while learning can increase the learning.

  3. Read the “There Are No Dumb Questions”

    That means all of them. They’re not optional sidebars—they’re part of the core content! Don’t skip them.

  4. Make this the last thing you read before bed. Or at least the last challenging thing.

    Part of the learning (especially the transfer to long-term memory) happens after you put the book down. Your brain needs time on its own, to do more processing. If you put in something new during that processing time, some of what you just learned will be lost.

  5. Drink water. Lots of it.

    Your brain works best in a nice bath of fluid. Dehydration (which can happen before you ever feel thirsty) decreases cognitive function.

  6. Talk about it. Out loud.

    Speaking activates a different part of the brain. If you’re trying to understand something, or increase your chance of remembering it later, say it out loud. Better still, try to explain it out loud to someone else. You’ll learn more quickly, and you might uncover ideas you hadn’t known were there when you were reading about it.

  7. Listen to your brain.

    Pay attention to whether your brain is getting overloaded. If you find yourself starting to skim the surface or forget what you just read, it’s time for a break. Once you go past a certain point, you won’t learn faster by trying to shove more in, and you might even hurt the process.

  8. Feel something!

    Your brain needs to know that this matters. Get involved with the stories. Make up your own captions for the photos. Groaning over a bad joke is still better than feeling nothing at all.

  9. Create something!

    Apply this to something new you’re designing, or rework an older project. Just do something to get some experience beyond the exercises and activities in this book. All you need is a pencil and a problem to solve…a problem that might benefit from programming.

  10. Get sleep.

    You’ve got to create a lot of new brain connections to learn to program. Sleep often; it helps.

Read Me

This is a learning experience, not a reference book. We deliberately stripped out everything that might get in the way of learning whatever it is we’re working on at that point in the book. And the first time through, you need to begin at the beginning, because the book makes assumptions about what you’ve already seen and learned.

We want you to learn the thinking process behind programming.

Some might call that computer science, but here’s a little secret: computer science isn’t a science and it’s not even all that much about computers (any more than astronomy is about telescopes). It’s a way of thinking, otherwise known these days as computational thinking, and once you learn to think computationally, you’ll be in a good position to apply that to any problem, environment, or programming language.

In this book we use Python.

Learning to drive without a vehicle is a little academic. And learning to think computationally without a programming language is more of a thought experiment than a marketable skill. So, in this book we use the very popular Python language. We’ll tell you more about its accolades in Chapter 2, but whether you’re a hobbyist or hoping to land a six-figure software development position, Python is a good place to start (and maybe end).

We don’t exhaustively cover every aspect of the Python language.

Not even close. There’s a lot you can learn about Python. This book is not a reference book, it’s a learning book, so it doesn’t cover everything there is to know about Python. Our goal is to teach you the fundamentals of coding and computational thinking so that you can pick up a book on any programming language and not feel totally lost.

You can use a Mac or PC, or Linux for that matter.

As Python is our primary vehicle used in this book and it is cross-platform, you can use whatever operating system you’re used to. Most of the screenshots in this book are from a Mac, but they should look similar on your PC or Linux box.

This book advocates well-structured and readable code based on best practices. You want to write code that you and other people can read and understand, code that will still work in next year’s version of Python. In this book we’re going to teach you to write clear, well-organized code from the get-go—code you can be proud of, code you’ll want to frame and put on the wall (just take it down before you bring your date over). The only thing that differs from what we’d write as professional code is that this book uses handwritten annotations next to code to explain what the code is doing. We found this works better in a learning book than traditional comments in code (if you have no idea what we’re talking about, you will; just give it a few chapters). But don’t worry because we’ll teach you how to document your code and we’ll show you examples of how we’d document our own code. All that said, we’re interested in teaching you to write code in the most straight-forward way so you can get the job done and move on to better things.


Annotations like this

Programming is serious business. You’re going to have to work, sometimes hard. A programmer has a different mindset, a different way of thinking about the world. At times you’re going to find coding very logical, while at other times it can be very abstract, if not downright mind bending. Some programming concepts take time to sink into your brain—you actually do have to sleep on them before you’ll get it. But no worries; we’re going to do all that in a brain-friendly way. Just take your time, give the concepts time to sink in, and go over the material multiple times if needed.

The activities are NOT optional.

The exercises and activities in this book are not add-ons; they’re part of the core content of the book. Some of them are to help with memory, some are for understanding, and some will help you apply what you’ve learned. If you skip them you will be missing large parts of the book (and you’ll probably be very confused). The crossword puzzles are the only things you don’t have to do, but they’re good for giving your brain a chance to think about the words in a different context.

The redundancy is intentional and important.

One distinct difference in a Head First book is that we want you to really get it. And we want you to finish the book remembering what you’ve learned. Most reference books don’t have retention and recall as a goal, but this book is about learning, so you’ll see some of the same concepts come up more than once.

The examples are as lean as possible.

Our readers tell us that it’s frustrating to wade through 200 lines of an example looking for the two lines they need to understand. Most examples in this book are shown within the smallest possible context, so that the part you’re trying to learn is clear and simple. Don’t expect all of the examples to be robust—they are written specifically for learning, and aren’t always fully functional. That said, for the larger examples we also try to make them fun, fascinating, and downright cool—something you’d want to show your friends and family.

We’ve placed all the example files on the web so you can download them. You’ll find them at http://wickedlysmart.com/hflearntocode.

The Brain Power exercises don’t usually have answers.

For some of them, there is no right answer, and for others, part of the learning experience of the Brain Power activities is for you to decide if and when your answers are right. In some of the Brain Power exercises, you will find hints to point you in the right direction.

Get the code examples, help, and discussion online.

You’ll find everything you need for this book online at http://wickedlysmart.com/hflearntocode, including code sample files and additional support material.


You’re going to have to install Python

More than likely your computer is either not going to have Python installed, or it’s not going to have the right version of Python installed. In this book we use Python 3, which at the time of writing was version 3.6. So, you’ll need to install version 3.6 or later. Here’s how:

  • For macOS, open your browser and enter:


On this page you should see the macOS download links. If not, look under the Downloads menu on the page.

  1. Click the Download button for Python 3.x (where x is the latest version). Do not download version 2.7.

  2. Once the installer is downloaded, open the installation package in your downloads folder and follow the installation instructions.

  3. After you’ve completed the install, navigate to your Applications folder, under which you’ll find the Python 3.x folder. To test your installation, double click the IDLE application in the Python 3.x folder:


    Note that you’ll need administrator privileges to install Python—if you commonly install apps, you should be fine; otherwise, ask your administrator for help.

  4. When the IDLE application appears on your screen, you should see something similar to the screenshot below. If not, recheck your installation for any errors that might have occurred.

  • For Windows, open your browser and enter:

  1. Click the Download button for Python 3.x (where x is the latest version). Do not download version 2.7.

  2. Choose to either save or run the executable installer. If the latter, click to run the installer after you’ve downloaded it.

  3. When you see the installer window appear on your screen, make sure the “Add Python to PATH” checkbox is checked at the bottom of the installer, then click “Install Now.”

  4. After you’ve completed the install, navigate using the Start button to All Programs, and in your list of apps you should see a menu option for Python 3.x (with your version number in place of the x). Under the Python menu you’ll see choices for Python 3.x, documentation, and IDLE, which is an editor we will also be using in this book.

  5. To test, click the IDLE menu item; when the IDLE application appears on your screen, you should see something similar to the screenshot below. If not, recheck your installation and any errors that might have occurred.


Note to Linux users: We’re not worried about you; let’s be real, you know what you’re doing. Just grab the approriate distribution from python.org

A word on organizing your code

Your source code is all the code you’ll be writing with this book. We recommend keeping your code organized on a per-chapter basis and throughout the book we’ve assumed that you’ll be creating one folder per chapter, like this:


You should also visit:


There you’ll find instructions for downloading the complete source code for the book. In this code you’ll find our versions of the programs you’re going to write as well as a few data files and images you’ll need. We do ask that you take the time to type in the programs yourself (this will help you develop your muscle memory for coding and help things sink into your brain), but if you run into any issues you just can’t figure out, you can always compare your code with ours to see where you might have made a mistake.



A huge thanks goes out first to my esteemed technical reviewers: Elisabeth Robson carefully and expertly reviewed the manuscript with a keen Head First and computer science eye. Josh Sharfman was the MVP reviewer who added depth and quality to every corner of the book. David Powers, in his usual style, rigorously scoured the technical text (his Harry Potter knowledge ain’t too shabby either). And veteran Head First author Paul Barry provided a much-needed Python critical eye. In addition, my review team (listed on the next page) was invaluable across every aspect of reviewing the book.


My biggest thanks to my editors, Jeff Bleiel, Dawn Schanafelt, and Meghan Blanchette. Meghan was instrumental in getting this book off the ground, Dawn carefully saw it through its early developmental stages, and Jeff drove the book through to its publication.

Also a big thanks to the entire O’Reilly team including Susan Conant, Rachel Roumeliotis, and Melanie Yarbrough. At WickedlySmart, thanks to Jamie Burton for all her help, including early reader surveys and managing the review team forum. And as always, thanks to Bert Bates and Kathy Sierra for inspiration, interesting discussion, and all their help solving writing conundrums. Thanks to Cory Doctorow for his support and for lending his writing to Chapter 9.

Finally, a number of individuals and organizations unknowingly inspired aspects of this book, including Daniel P. Friedman, Nathan Bergey, the Raspberry Pi Foundation, and Socratica.


*The large number of acknowledgments is because we’re testing the theory that everyone mentioned in a book acknowledgment will buy at least one copy, probably more, what with relatives and everything. If you’d like to be in the acknowledgment of our next book, and you have a large family, write to us.

The Review Team

Meet the review team!

An amazing group of people took on reviewing this book. With backgrounds from newbie to expert, and professions as diverse as architect, dentist, elementary school teacher, real estate agent, and AP computer science teacher, they participated across the globe from Albania to Australia, from Kenya to Kosovo, from the Netherlands to Nigeria to New Zealand.

This group read every page, did every exercise, and entered and executed every line of code, providing feedback and encouragement over 600 pages. They also, on their own, worked as a team, helping each other through new concepts, double-checking errors, and locating problems in the text and code.

Every reviewer here made significant contributions to this book and vastly improved its quality.

Thank you!


Also a big thanks to Christopher Davies, Constance Mallon, and Wanda Hernandez for their significant contributions to this book.

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