Getting Started with Python Classes Methods, Attributes, and Usage

In Python, a class is a blueprint for creating objects.

This guide demonstrates a basic example of a class in Python where the properties of a chair, such as legs and handle, are defined as attributes, and its functionality is represented by a method called feature.

Basic Class Example

class Chair:
    legs = 4
    handle = 2

    def feature(self):
        print("You can sit")

In this example:

• legs and handle are attributes of the Chair class.
• lges is also class variable, becasue this will be available to all of the instance of Chair class.
• feature is a method that describes what the chair can do.

Using the Chair Class

Now, let's create an instance of the Chair class and use its method.

class Chair:
    legs = 4
    handle = 2

    def feature(self):
        print(f"You can sit, and it has {self.legs} legs")

chair_instance = Chair()
chair_instance.feature()

Here:

• We created an instance of the Chair class and stored it in chair_instance.
• We then called the feature method, which uses f-string (formatted string literal) to include the number of legs in the output.

The Special Method (Constructor)

The __init__ method, also known as the constructor, allows you to set the initial state of an object when it is created.

class Chair:
    def __init__(self, name):
        self.name = name  # The __init__ method initializes the object's state
        print(name)

    legs = 4
    handle = 2

    def feature(self):
        print(f"You can sit, and it has {self.legs} legs")

chair_instance = Chair('Wooden chair')
chair_instance.feature()

Here:

• The __init__ method takes self (reference to the current object) and name as parameters.
• name is an attribute of the Chair class. For every instance the name will be different and it is instance specific
• When a new instance is created, __init__ is called automatically, setting the initial state of the object.

Constant or Class Attributes

Attributes like legs and handle are called class attributes because they belong to the class itself, not to any specific instance. This means that all objects created from the Chair class will share these attributes.

class Chair:
    legs = 4
    handle = 2

    def feature(self):
        print("You can sit")

Class Method - @classmethod

A class method is a method that is bound to the class and not the instance of the class. You can use the @classmethod decorator to create a class method. Here’s an example:

class Chair:
    def __init__(self, name):
        self.name = name
        print(f"New chair added as {name}")
        Chair.add_chair()  # Calling the class method

    legs = 4
    handle = 2
    number_of_chair = 0

    def feature(self):
        print(f"You can sit, and it has {self.legs} legs")

    @classmethod
    def add_chair(cls):
        cls.number_of_chair += 1
        print(f"Total number of chairs: {cls.number_of_chair}")

chair_instance1 = Chair('Wooden chair')
chair_instance2 = Chair('Steel chair')

Here:

• add_chair is a class method because it uses the @classmethod decorator.
• It uses cls as an argument, which refers to the class itself (Chair). Class methods typically perform operations that affect the class as a whole, such as modifying class-level attributes.

Output:

New chair added as Wooden chair
Total number of chairs: 1
New chair added as Steel chair
Total number of chairs: 2

Function vs. Method

• Function: A function in Python is a block of reusable code defined using the def keyword. Functions can be called independently and are not bound to any object or class.

  def greet():
      print("Hello!")
  
  greet()

• Method: A method is a function defined inside a class and is bound to instances of that class. Methods operate on the instance's data (attributes) and require the self parameter to refer to the instance calling the method.

  class Person:
      def greet(self):  # 'self' refers to the instance calling this method
          print("Hello!")
  
  person_instance = Person()
  person_instance.greet()  # Calling a method