A brief introduction to programming

We love to make references to the real world when we teach coding; we believe they help people to better retain the concepts they are learning. However, now is the time to be a bit more rigorous and see what coding is from a more technical perspective.

When we write code, we are instructing a computer about the things it has to do. Where does the action happen? In many places: the computer memory, hard drives, network cables, the CPU, and so on. It is a whole world, which most of the time is the representation of a subset of the real world.

If you write a piece of software that allows people to buy clothes online, you will have to represent real people, real clothes, real brands, sizes, and so on and so forth, within the boundaries of a program.

To do this, you will need to create and handle objects in your program. A person can be an object. A car is an object. A pair of trousers is an object. Luckily, Python understands objects very well.

The two key features any object has are properties and methods. Let us take the example of a person as an object. Typically, in a computer program, you will represent people as customers or employees. The properties that you store against them are things like a name, a social security number, an age, whether they have a driving license, an email, and so on. In a computer program, you store all the data needed in order to use an object for the purpose that needs to be served. If you are coding a website to sell clothes, you probably want to store the heights and weights as well as other measures of your customers so that the appropriate clothes can be suggested to them. So, properties are characteristics of an object. We use them all the time: Could you pass me that pen? —Which one? —The black one. Here, we used the color (black) property of a pen to identify it (most likely it was being kept alongside different colored pens for the distinction to be necessary).

Methods are actions that an object can perform. As a person, I have methods such as speak, walk, sleep, wake up, eat, dream, write, read, and so on. All the things that I can do could be seen as methods of the objects that represent me.

So, now that you know what objects are, that they provide methods that can be run and properties that you can inspect, you are ready to start coding. Coding, in fact, is simply about managing those objects that live in the subset of the world we’re reproducing in our software. You can create, use, reuse, and delete objects as you please.

According to the Data Model chapter on the official Python documentation (https://docs.python.org/3/reference/datamodel.html):

“Objects are Python’s abstraction for data. All data in a Python program is represented by objects or by relations between objects.”

We will take a closer look at Python objects in Chapter 6, OOP, Decorators, and Iterators. For now, all we need to know is that every object in Python has an ID (or identity), a type, and a value.

Once created, the ID of an object never changes. It is a unique identifier for it, and it is used behind the scenes by Python to retrieve the object when we want to use it. The type also never changes. The type states what operations are supported by the object and the possible values that can be assigned to it. We will see Python’s most important data types in Chapter 2, Built-In Data Types. The value of some objects can change. Such objects are said to be mutable. If the value cannot be changed, the object is said to be immutable.

How, then, do we use an object? We give it a name, of course! When you give an object a name, then you can use the name to retrieve the object and use it. In a more generic sense, objects, such as numbers, strings (text), and collections, are associated with a name. In other languages, the name is normally called a variable. You can see the variable as being like a box, which you can use to hold data.

Objects represent data. It is stored in databases or sent over network connections. It is what you see when you open any web page, or work on a document. Computer programs manipulate that data to perform all sorts of actions. They regulate its flow, evaluate conditions, react to events, and much more.

To do all this, we need a language. That is what Python is for. Python is the language we will use together throughout this book to instruct the computer to do something for us.