What is OOP?

OOP stands for Object-Oriented Programming.

Python is an object-oriented language, allowing you to structure your code using classes and objects for better organization and reusability.

Advantages of OOP

• Provides a clear structure to programs
• Makes code easier to maintain, reuse, and debug
• Helps keep your code DRY (Don't Repeat Yourself)
• Allows you to build reusable applications with less code

Tip: The DRY principle means you should avoid writing the same code more than once. Move repeated code into functions or classes and reuse it.

What are Classes and Objects?

Classes and objects are the two core concepts in object-oriented programming.

A class defines what an object should look like, and an object is created based on that class. For example:

When you create an object from a class, it inherits all the variables and functions defined inside that class.

Python Classes/Objects

Python is an object oriented programming language.

Almost everything in Python is an object, with its properties and methods.

A Class is like an object constructor, or a "blueprint" for creating objects.

Create a Class

To create a class, use the keyword class:

Example

Create a class named MyClass, with a property named x:

class MyClass:
  x = 5

Create Object

Now we can use the class named MyClass to create objects:

Example

Create an object named p1, and print the value of x:

p1 = MyClass()
print(p1.x)

Delete Objects

You can delete objects by using the del keyword:

Example

Delete the p1 object:

del p1

Multiple Objects

You can create multiple objects from the same class:

Example

Create three objects from the MyClass class:

p1 = MyClass()
p2 = MyClass()
p3 = MyClass()

print(p1.x)
print(p2.x)
print(p3.x)

Note: Each object is independent and has its own copy of the class properties.

The pass Statement

class definitions cannot be empty, but if you for some reason have a class definition with no content, put in the pass statement to avoid getting an error.

The __init__() Method

All classes have a built-in method called __init__(), which is always executed when the class is being initiated.

The __init__() method is used to assign values to object properties, or to perform operations that are necessary when the object is being created.

Example

Create a class named Person, use the __init__() method to assign values for name and age:

class Person:
  def __init__(self, name, age):
    self.name = name
    self.age = age

p1 = Person("Emil", 36)

print(p1.name)
print(p1.age)

Note: The __init__() method is called automatically every time the class is being used to create a new object.

Why Use __init__()?

Without the __init__() method, you would need to set properties manually for each object:

Example

Create a class without __init__():

class Person:
  pass

p1 = Person()
p1.name = "Tobias"
p1.age = 25

print(p1.name)
print(p1.age)

Using __init__() makes it easier to create objects with initial values:

Example

With __init__(), you can set initial values when creating the object:

class Person:
  def __init__(self, name, age):
    self.name = name
    self.age = age

p1 = Person("Linus", 28)

print(p1.name)
print(p1.age)

Default Values in __init__()

You can also set default values for parameters in the __init__() method:

Example

Set a default value for the age parameter:

class Person:
  def __init__(self, name, age=18):
    self.name = name
    self.age = age

p1 = Person("Emil")
p2 = Person("Tobias", 25)

print(p1.name, p1.age)
print(p2.name, p2.age)

Multiple Parameters

The __init__() method can have as many parameters as you need:

Example

Create a Person class with multiple parameters:

class Person:
  def __init__(self, name, age, city, country):
    self.name = name
    self.age = age
    self.city = city
    self.country = country

p1 = Person("Linus", 30, "Oslo", "Norway")

print(p1.name)
print(p1.age)
print(p1.city)
print(p1.country)