Classes

A class is a user-defined template for creating objects.

It bundles data and functions together, making it easier to manage and use them. When we create a new class, we define a new type of object. We can then create multiple instances of this object type.

For example, we could create a class representing a 1994 Toyota Hilux Surf (The greatest car ever assembled).

Creating a Class

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Classes are defined using the class keyword, followed by the class name and a colon. We can then define attributes inside the class to represent properties of the object.

class HiluxSurf:

    make = "Toyota"
    model = "Hilux Surf"
    year = 1994

Here, make, model, and year are class attributes, they describe information that is shared by every HiluxSurf object we create.

Objects

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An object is a specific instance of a class.

Multiple objects can be created from the same class, with each object representing its own individual thing.

Let’s create an object from our HiluxSurf class.

class HiluxSurf:

    make = "Toyota"
    model = "Hilux Surf"
    year = 1994


# Creating an object from the class
surf1 = HiluxSurf()

print(surf1.make)
print(surf1.model)
print(surf1.year)

Output:

Toyota
Hilux Surf
1994

Explanation: make, model, and year are class attributes. They are shared across all instances of the HiluxSurf class.

Initialise an Object with __init__()

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What if we want to create multiple Hilux Surfs, but give each one different properties? For example, one might be red while another is baby blue.

This is where __init__() comes in.

The __init__() method is automatically called when an object is created. It allows us to initialise the object’s attributes with values provided when the object is created.

class HiluxSurf:

    make = "Toyota"
    model = "Hilux Surf"
    year = 1994

    def __init__(self, colour, engine):

        self.colour = colour
        self.engine = engine

We can now create individual Hilux Surfs with their own colours and engines.

surf1 = HiluxSurf("Red", "3.0L Diesel")

surf2 = HiluxSurf("Baby Blue", "2.4L Diesel")

print(surf1.colour)
print(surf2.colour)

Output:

Red
Baby Blue

Both objects are instances of the same class, but they have their own instance attributes.

What is self?

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self refers to the current object - When we write:

self.colour = colour

we are saying:

Store the value of colour inside this particular object.

So when we create:

surf1 = HiluxSurf("Red", "3.0L Diesel")

surf1.colour becomes "Red".

And when we create:

surf2 = HiluxSurf("Baby Blue", "2.4L Diesel")

surf2.colour becomes "Baby Blue".

The two objects therefore contain different values, even though they were created from the same class.

__str__() Method

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The __str__() method allows us to define a custom string representation of an object. By default, if we print an object, Python will produce something like:

<__main__.HiluxSurf object at 0x00000123>

Nice. (Not really). Therefore, we define our own __str__() method to make the output more readable.

class HiluxSurf:

    make = "Toyota"
    model = "Hilux Surf"
    year = 1994

    def __init__(self, colour, engine):

        self.colour = colour
        self.engine = engine

    def __str__(self):

        return f"{self.year} {self.make} {self.model} - {self.colour}, {self.engine}"

Now we can create our objects and print them.

surf1 = HiluxSurf("Red", "3.0L Diesel")

surf2 = HiluxSurf("Baby Blue", "2.4L Diesel")

print(surf1)
print(surf2)

Output:

1994 Toyota Hilux Surf - Red, 3.0L Diesel
1994 Toyota Hilux Surf - Baby Blue, 2.4L Diesel

When we call:

print(surf1)

Python automatically calls the object’s __str__() method.

This lets us control how our objects are represented when they are converted into strings.