Chapter 1
How a Computer Works

1.1 Introduction

In today's society, almost every task requires the use of a computer. In schools, students use computers to search the Internet and to send emails. At work, people use them to make presentations, to analyze data, and to communicate with customers. At home, people use computers to play games, to connect to social networks and to chat with other people all over the world. Of course, don't forget smartphones such as iPhones. They are computers as well!

Computers can perform so many different tasks because of their ability to be programmed. In other words, a computer can perform any job that a program tells it to. A program is a set of statements (often called instructions or commands) that a computer follows in order to perform a specific task.

Programs are essential to a computer, because without them a computer is a dummy machine that can do nothing at all. It is the program that actually tells the computer what to do and when to do it. On the other hand, the programmer or the software developer is the person who designs, creates, and often tests computer programs.

This book introduces you to the basic concepts of computer programming using the Python language.

1.2 What is Hardware?

The term hardware refers to all devices or components that make up a computer. If you have ever opened the case of a computer or a laptop you have probably seen many of its components, such as the microprocessor (CPU), the memory, and the hard disk. A computer is not a device but a system of devices that all work together. The basic components of a typical computer system are discussed here.

This is the part of a computer that actually performs all the tasks defined in a program (basic arithmetic, logical, and input/output operations).

This is the area where the computer holds the program (while it is being executed/run) as well as the data that the program is working with. All programs and data stored in this type of memory are lost when you shut down your computer or you unplug it from the wall outlet.

ROM or Read Only Memory is a special type of memory which can only be read by the computer (but cannot be changed). All programs and data stored in this type of memory are not lost when the computer is switched off. ROM usually contains manufacturer's instructions as well as a program called the bootstrap loader whose function is to start the operation of computer system once the power is turned on.

This is usually the hard disk or the SSD (Solid State Drive), and sometimes (but more rarely) the CD/DVD drive. In contrast to main memory (RAM), this type of memory can hold data for a longer period of time, even if there is no power to the computer. However, programs stored in this memory cannot be directly executed. They must be transferred to a much faster memory; that is, the main memory.

Input devices are all those devices that collect data from the outside world and enter them into the computer for further processing. Keyboards, mice, and microphones are all input devices.

Output devices are all those devices that output data to the outside world. Monitors (screens) and printers are output devices.

1.3 What is Software?

Everything that a computer does is controlled by software. There are two categories of software: system software and application software.

1.4 How a Computer Executes (Runs) a Program

When you turn on your computer, the main memory (RAM) is completely empty. The first thing the computer needs to do is to transfer the operating system from the hard disk to the main memory.

After the operating system is loaded to main memory, you can execute (run) any program (application software) you like. This is usually done by clicking, double clicking, or tapping the program's corresponding icon. For example, let's say you click on the icon of your favorite word processor. This action orders your computer to copy (or load) the word processing program from your hard disk to the main memory (RAM) so the CPU can execute it.

1.5 Compilers and Interpreters

Computers can execute programs that are written in a strictly defined computer language. You cannot write a program using a natural language such as English or Greek, because your computer won't understand you!

But what does a computer actually understand? A computer can understand a specific low-level language called the machine language. In a machine language all statements (or commands) are made up of zeros and ones. The following is an example of a program written in a machine language, that calculates the sum of two numbers.

Shocked? Don't worry, you are not going to write programs this way. Hopefully, no one writes computer programs this way anymore. Nowadays, all programmers write their programs in a high-level language and then they use a special program to translate them into a machine language.

There are two types of programs that programmers use to perform translation: compilers and interpreters.

A compiler is a program that translates statements written in a high-level language into a separate machine language program. You can then execute the machine language program any time you wish. After the translation, there is no need to run the compiler again unless you make changes in the high-level language program.

An interpreter is a program that simultaneously translates and executes the statements written in a high-level language. As the interpreter reads each individual statement in the high-level language program, it translates it into a machine language code and then directly executes it. This process is repeated for every statement in the program.

1.6 What is Source Code?

The statements (often called instructions or commands) that the programmer writes in a high-level language are called source code or simply code. The programmer first types the source code into a program known as a code editor, and then uses either a compiler to translate it into a machine language program, or an interpreter to translate and execute it at the same time.

1.7 Review Questions: True/False

Choose true or false for each of the following statements.

1.8 Review Questions: Multiple Choice

Select the correct answer for each of the following statements.

Chapter 2
Python and Integrated Development Environments

2.1 What is Python?

Python is a widely used general-purpose, high-level computer programming language that allows programmers to create applications, web pages, and many other types of software.

Python is often referred to as a scripting language despite the fact that the official website says that it's a programming language. The truth, of course, is somewhere in the middle. Python can be used either as a scripting language, or a programming language!

2.2 What is the Difference Between a Script and a Program?

Technically speaking, a script is interpreted whereas a program is compiled, but this is actually not their major difference. There is another more important difference between them!

The main purpose of a script written in a scripting language such as JavaScript, or VBA (Visual Basic for Applications) is to control another application. So you can say that, in some ways JavaScript controls the web browser, and VBA controls a Microsoft^® Office application such as MS Word or MS Excel.

On the other hand, a program written in a programming language such as Python, C++, or Java (to name a few) executes independently of any other application. A program is executed as stand-alone any time the user wishes without the need of a hosting application.

2.3 Why You Should Learn Python

Python is what is known as a “high-level” computer language. Python's coding style is very easy to understand. It is a flexible and powerful language, making it well-suited for developing medium-scale applications or dynamic web pages. It is the perfect language for teaching programming, especially at the introductory level, and it is widely used in scientific and numerical computing.

One of Python's capabilities is the ability to interact with the file system of a computer. Python can create files, write in files, or read the contents from files. It can also create directories, copy files, delete files, rename files, or even change file attributes. Python can perform almost any task related to the file system, making it suitable even for system administration tasks. For example, you can write a Python program to back up your files or a program that processes text files by reformatting their contents.

Moreover, Python can execute system commands or any other program installed on your system. Thus, programs written and compiled in C, C++, Java, or any other computer language can be executed from Python and Python can make use of their output. This enables you to add functionality to your Python programs without spending time rewriting your old ones.

There are millions—probably even billions—of lines of code already written in Python and your possibilities for code reuse are huge! This is why many people prefer using Python to any other programming language. This is also a very good reason why you should actually learn Python!

2.4 How Python Works

Computers do not understand natural languages such as English or Greek, so you need a computer language such as Python to communicate with them. Python is a very powerful high-level computer language. The Python interpreter (or, actually, a combination of a compiler and an interpreter) converts Python language to a language that computers can actually understand, and that is known as the “machine language”.

In the past, computer languages made use of either an interpreter or a compiler. Nowadays however, many computer languages including Python use both a compiler and an interpreter. The Python compiler translates Python statements into bytecode statements and saves them in a .pyc file. Later, when a user wants to execute the file, the interpreter (often called Python Virtual Machine or Python VM) converts the bytecode into low-level machine language code for direct execution on the hardware.

In Figure 2–1 you can see how statements written in Python are compiled into bytecode and how bytecode is then executed using interpretation.

.

Figure 2–1 Executing Python statements using the Python Virtual Machine

Now come some reasonable questions: Why all this trouble? Why does Python and other languages (such as C#) translate twice? Why are Python statements not directly translated into low-level machine language code? The answer lies in the fact that Python is designed to be a platform-independent programming language. This means that a program is written once but it can be executed on any device, regardless of its operating system or its architecture, as long as the appropriate version of Python is installed on it. In the past, programs had to be recompiled, or even rewritten, for each computer platform. One of the biggest advantages of Python is that you only have to write and compile a program once! In Figure 2–2 you can see how statements written in Python are compiled into bytecode and how bytecode can then be executed on any platform that has the appropriate version of Python installed on it.

Figure 2–2 Executing Python statements on different platforms

Efficiency is another reason why Python statements are not directly translated into low-level machine language code because:

To write and execute Python programs, you need to install two software applications: a Python interpreter and an Integrated Development Environment (IDE). The IDE is necessary for writing Python programs, while the Python interpreter is required for executing them.

2.5 Integrated Development Environments

An Integrated Development Environment, or IDE, is a type of software that includes all the basic tools programmers need to write and test programs. An IDE typically contains a source code editor and integrates tools such as a compiler or an interpreter, along with a debugger. IDLE and Visual Studio Code are examples of IDEs that let programmers write, execute and debug their source code.

2.6 IDLE

IDLE is an Integrated Development Environment (IDE) that provides a very simple environment suitable for beginners, especially in an educational setting. With IDLE, novice programmers can effortlessly write and execute their Python programs.

In Windows, the IDLE module is included by default in the Python installer and will be installed when you follow the steps outlined in the next chapter (Chapter 3). Additionally, in Chapter 9, you will be guided on how to use IDLE to write, execute and debug Python programs. You will also learn numerous tips and tricks that will be valuable in your first steps as a budding programmer!

2.7 Microsoft Visual Studio

Microsoft Visual Studio is an Integrated Development Environment (IDE) that provides a great set of tools for many programming languages (via extensions installed separately) and lets you easily create applications for Android, iOS, macOS, Windows, and the cloud, as well as websites, web applications, and web services.

Visual Studio is much more than a text editor. It can indent lines, match words and brackets, and highlight source code that is written incorrectly. It also provides automatic code (IntelliSense^®), which means that as you type, it displays a list of possible completions. The IDE also provides hints to help you analyze your code and find any potential problems. It even suggests some simple solutions to fix those problems. You can use the Visual Studio not only to write but also to execute your programs directly from the IDE.

Visual Studio has a large community of users all around the world and this is why it comes in so many different flavors. Specifically, in Microsoft's download page you can download:

In the next chapter (Chapter 3), you will find links guiding you to instructions on how to install and configure whatever is necessary on your computer, such as the Python interpreter, and IDLE or Visual Studio Code, on either Windows or Linux. Then, in Chapter 9, you will discover guidance on using IDLE or Visual Studio Code to write, execute and debug Python programs. These instructions are available on my website. Additionally, you will find numerous tips and tricks there that will be valuable in your first steps as a budding programmer!

Chapter 3
Software Packages to Install

3.1 What to Install

For the purposes of this book, you need to install Python and an Integrated Development Environment (IDE) on your computer. IDLE and Visual Studio Code are examples of such IDEs. It's up to you to choose which one you are going to use. If you have decided to use IDLE, then you can skip setting up Visual Studio Code.

All the instructions you need regarding how to set up Python, and IDLE or Visual Studio Code, on either Windows or Linux are maintained on my website at the following addresses. This gives me the flexibility to review them frequently and keep them up-to-date.

https://tinyurl.com/2uh4xxm5

https://www.bouraspage.com/python-setup-write-execute-debug

.

If you find any inconsistencies, please let me know, and I will update the instructions as soon as possible. To report issues, visit one of the following addresses:

https://tinyurl.com/28nwh2nf

https://www.bouraspage.com/report-errata

.

Review in “Introductory Knowledge”

Review Crossword Puzzles

Across

1) Statements or commands.

3) Windows is such a system.

4) A computer component.

6) A category of software.

8) An input device.

11) It's the person who designs computer programs.

14) An output device.

15) Antivirus is such a software.

16) In today's society, almost every task requires the use of this device.

17) A computer component.

18) All these devices make up a computer.

Down

2) These devices are also computers.

5) Computers can perform so many different tasks because of their ability to be _____________.

7) Special memory that can only be read.

9) A secondary storage device.

10) A browser is this type of software.

12) An input device.

13) An operating system.

Across

3) A category of programming language.

4) In a machine language all statements are made up of zeros and _______.

8) Widely used general-purpose, high-level computer programming language.

9) The statements that a programmer writes to solve a problem.

12) The CPU performs one of these basic operations.

13) All data stored in this type of memory are lost when you shut down your computer.

14) Python __________ Machine converts the bytecode into low-level machine language code.

16) A low-level language.

Down

1) A program that simultaneously translates and executes the statements written in a high-level language.

2) Python __________ is a machine language executed by the Python Virtual Machine.

5) A scripting language.

6) A set of statements.

7) Run a program.

10) This software controls a device that is attached to your computer.

11) A program that translates statements written in a high-level language into a separate machine language program.

15) IDLE is such a software.

Across

3) A scripting language that can control Microsoft Word.

6) An intermediate language that C# uses.

7) A program that translates statements written in a high-level computer language into a separate machine language program.

8) Python can execute ___________ commands .

9) A script requires a __________ application in order to execute.

10) An input device.

12) One reason why Python statements are not directly translated into low-level machine language code.

Down

1) Scripts written in VBA.

2) One of Python's capabilities is the ability to interact with the _______ system of a computer.

4) It displays data to the user.

5) It performs logical operations.

11) Visual Studio Code is such a software

Review Questions

Answer the following questions.