A Profound Introduction

Welcome to the most straightforward and intuitive blog on Object-Oriented Programming (OOP) that you'll ever find on dev.to. This blog series, Part #1, aims to provide you with a clear understanding of the subject.

Let's Begin

We'll start with a code block in Python:

l = [1, 2, 3, 4, 5]
print(l.upper())

What do you think the output would be? Surprisingly, this will result in an error:

'list' object has no attribute 'upper'

Now, let's focus on two critical terms here: "object" and "attribute."

You might be wondering why the error refers to the list: l as an "object" when you have learned that a list is a datatype 🤔. Additionally, what does "attribute" mean? Let's explore further with another code block:

l = [1, 2, 3, "oops"]
print(type(l))
# Output: <class 'list'>

Interesting, right? When we try to get the type of the list, it says "l belongs to the class 'list'." But what is a "class" exactly?

Moments ago, we saw that an error mentioned that 'list' was an object. Let's clarify this confusion.

Class, Object, and Attributes

Here's the moment of truth: every datatype you've encountered in Python is, in fact, a class.

What is a class?

You can think of a class as a blueprint, but what do I exactly mean by a blueprint? We'll soon find out.

So, every datatype is a class, and whenever we create a variable of a class (datatype), it is referred to as an object.

By the way, now that we know datatypes are classes, and since they were already present, datatypes are known as built-in classes. On the other hand, we have user-defined classes, which we'll explore in another blog.

Hence, if you try to print type(12), the output would be class <int>. And if you create an object of the class/datatype int:

n = 1234  # n is an object of datatype int
print(n.append(1))

The above code will result in an error:

AttributeError: 'int' object has no attribute 'append'

This error informs us that the object we created n is referred to as an object of the int class/datatype.

In simpler terms, an object is an instance of a class.

We know that we can't append to an int, but why?

Because whoever created the class int or datatype int didn't add a functionality to do so. The functionality of an object, or the functions that we can perform on an object of a particular class, is called an attribute.

In the above code's output, you may see the error message:
AttributeError: 'int' object has no attribute 'append'

This indicates that the int object n here, of class int, doesn't have any functionality to append.

That's all for now! We'll cover more topics soon, so stay tuned, buddy!