A proper introduction
I love to make references to the real world when I teach coding; I believe they help people retain the concepts better. 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're 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's 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.
In order to do so, you will need to create and handle objects in the program you're writing. A person can be an object. A car is an object. A pair of socks is an object. Luckily, Python understands objects very well.
The two main features any object has are properties and methods. Let's take a person object as an example. Typically in a computer program, you'll represent people as customers or employees. The properties that you store against them are things like the name, the SSN, the age, if they have a driving license, their email, gender, and so on. In a computer program, you store all the data you need in order to use an object for the purpose you're serving. 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 you can suggest the appropriate clothes for 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 black property of a pen to identify it (most likely among a blue and a red one).
Methods are things that an object can do. 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 and that they expose methods that you can run and properties that you can inspect, you're ready to start coding. Coding in fact is simply about managing those objects that live in the subset of the world that 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'll take a closer look at Python objects in Chapter6, 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 is never changed. It's a unique identifier for it, and it's used behind the scenes by Python to retrieve the object when we want to use it.
The type, as well, never changes. The type tells what operations are supported by the object and the possible values that can be assigned to it.
We'll see Python's most important data types in Chapter 2, Built-in Data Types.
The value can either change or not. If it can, the object is said to be mutable, while when it cannot, the object is said to be immutable.
How 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), collections, and so on are associated with a name. Usually, we say that this name is the name of a variable. You can see the variable as being like a box, which you can use to hold data.
So, you have all the objects you need; what now? Well, we need to use them, right? We may want to send them over a network connection or store them in a database. Maybe display them on a web page or write them into a file. In order to do so, we need to react to a user filling in a form, or pressing a button, or opening a web page and performing a search. We react by running our code, evaluating conditions to choose which parts to execute, how many times, and under which circumstances.
And to do all this, basically we need a language. That's what Python is for. Python is the language we'll use together throughout this book to instruct the computer to do something for us.
Now, enough of this theoretical stuff; let's get started.
