# 1.6. How to Use This Book¶

As you progress through the rest of the book, don’t be afraid if the concepts don’t seem to fit together well the first time. When you were learning to speak, it was not a problem for your first few years that you just made cute gurgling noises. And it was OK if it took six months for you to move from simple vocabulary to simple sentences and took several more years to move from sentences to paragraphs, and a few more years to be able to write an interesting complete short story on your own.

We want you to learn Python much more rapidly, so we teach it all at the same time over the next few chapters. But it is like learning a new language that takes time to absorb and understand before it feels natural. That leads to some confusion as we visit and revisit topics to try to get you to see the big picture while we are defining the tiny fragments that make up that big picture. While the book is written linearly, and if you are taking a course it will progress in a linear fashion, don’t hesitate to be very nonlinear in how you approach the material. Look forwards and backwards and read with a light touch. By skimming more advanced material without fully understanding the details, you can get a better understanding of the “why?” of programming. By reviewing previous material and even redoing earlier exercises, you will realize that you actually learned a lot of material even if the material you are currently staring at seems a bit impenetrable.

Usually when you are learning your first programming language, there are a few wonderful “Ah Hah!” moments where you can look up from pounding away at some rock with a hammer and chisel and step away and see that you are indeed building a beautiful sculpture.

If something seems particularly hard, there is usually no value in staying up all night and staring at it. Take a break, take a nap, have a snack, explain what you are having a problem with to someone (or perhaps your dog), and then come back to it with fresh eyes. I assure you that once you learn the programming concepts in the book you will look back and see that it was all really easy and elegant and it simply took you a bit of time to absorb it.

# 1.7. Conventions Used in This Book¶

So we are about to start diving into how to code. But before we teach you to code, we need to teach you how to read this book. The first thing we need to teach you to do is to be able to tell the difference between when we are talking to you about regular text and when we are talking to you about code.

## 1.7.1. code inline with text¶

Text formatted like this: variable1 is used to indicate Python code. Python code is how we will be telling the computer what to do. In this book we will sometimes be mixing words meant to be read as code into regular sentences.

For example:

The program’s last variable is unused.

The program’s last variable is unused.

These sentences have very different meanings. The first sentence is talking about a variable named unused that is the final variable in the program. The second sentence is referring to a variable named last that is never used in the program.

## 1.7.2. Active code¶

Interactive, “live” code blocks called “Active Code” are included throughout the book. These allow you to run the code and see the programs output immediately next to the block. You can also modify the code to try new things and see what happens. The “Active Code” is a great way for you to check your understanding of the material.

We encourage you to look at the code in each block before you run it and try to make a prediction about what will happen when you do. If it doesn’t do quite what you thought, it’s worth figuring out why and paying attention to all of the bits of the code. In programming, the details really matter. The Active Code blocks are there to help you figure out the details.

Don’t be hesitant to mess around and change the Code Blocks. Each block keeps track of changes you’ve made and lets you change it back to a previous version using a slider bar under the block.

If you want to keep your code, you can also click the “download” button in the block.

Try out an Active Code Block for yourself. Run the code below, then change what it prints and run it again. Drag the slider that appears below to undo your changes.

The “Show CodeLens” will bring up the block’s code in an interactive tool called Online Python Tutor that allows you to visualize what the code is doing, step-by-step and line-by-line. For the above program, this isn’t very interesting, because it is a single, simple line. For any later code that is not immediately obvious, though, using this “CodeLens” can help you gain a much better understanding of how the code works.

## 1.7.3. Static code; >>> prompts¶

Some blocks of code are included in non-interactive blocks that you can’t change. Non-interactive blocks look like this:

word1 = "Hello"
word2 = "world"
print(word1, word2)


And sometimes, when we want to show the result of some code along with the code itself, we’ll use this: >>>

>>> word1 = "Hello"
>>> word2 = "world"
>>> print(word1, word2)
Hello world


In the block above the first three lines are individual lines of instructions that were sent to the computer. And the fourth line is the result the computer returned.

Why use the >>>? Well, one way programmers interact with computers is by using a read-evaluate-print loop (REPL). A REPL is software that reads a line of code typed in by a user, evaluates it to determine its value, and prints that value back to the user. The >>> is a prompt commonly used in Python REPLs. It’s like saying ‘Enter your code here.’

So the example above includes three lines entered by the user (the first three with the >>> prompts). The first two lines did not print anything, because (as we’ll see soon), they are assignments that don’t output or produce any value themselves. The last line entered by the user, print(word1, word2) does have an output below it, which is the result of evaluating that line.

If you want to try out a Python REPL yourself, you can access one online at https://www.python.org/shell/. Or, if you have Python installed on your own computer, you may be able to access its REPL by running the python3 command in a Terminal or Command Prompt (details depend on your operating system).

## 1.7.4. Syntax patterns¶

A critical piece of learning a programming langauge is knowing its syntax. The syntax of a language is the set of rules that specify what is a valid program and what is not. Any program that does not follow all of the syntax rules of its language cannot be run.

Throughout this book, we will present syntax patterns each time we present a new piece of Python’s syntax. They will look like this:

Syntax Pattern

Details of the pattern will go here.

These are formal, precise rules about how Python must be written. It’s worth memorizing their details (there aren’t many, to be honest) and keeping them in mind whenever you are writing your own code or reading someone else’s.