Creating a Class

How do we create a class?

To create a class, we can use the class keyword to define the data structures (attributes) and methods (behaviours or operations that can act on the data structures of that object):

1. Class Definition

class class_name:
	...
	# Use 'pass' as a placehodler if the class body is  empty for now

Optional docstring

We can provide an additional docstring after the class definition to provide information about the class.

class <class_name>:
	'''<optional_docstring>'''

2. Adding a Constructor (`init)` Method

Define the __init__ method within the class to initialize and define the attributes when an object is created. This method is called a constructor:

class ClassName:
	''' Optional doc string of the class'''

    def __init__(self, attribute1, attribute2, ...):
        # Initialize attributes: self.instance_var
        self.attribute1 = attribute1 #initial value for attribute1 passed
        self.attribute2 = attribute2 #initial value for attribute2 passed
        # ...

Why is this important?

The primary purpose of the constructor function is to initialize the attributes of an object. This ensures that every object created from the class starts with defined initial state.

What is the self parameter?

The self parameter (you could choose any other name, but nobody ever does!) is automatically set to reference the newly created object that needs to be initialized.

Defining default values

You can provide default values for attributes in the __init__ method. This allows creating objects with some attributes set to default values if they are not explicitly provided during object creation

class Rectangle:
    def __init__(self, length=0, width=0): # defining default values
        self.length = length # length = 0 if no other value is specified by user
        self.width = width

3. Adding a Behaviours to a Class

To define methods within the class to represent the behaviors or actions that objects can perform, we can follow the process of creating a user-defined functions. Note: self is passed as the first parameter explicitly every single time we define a method.

class ClassName:
	''' Optional doc string of the class'''

    def __init__(self, attribute1, attribute2, ...):
        # Initialize attributes: self.instance_var
        self.attribute1 = attribute1 #initial value for attribute1 passed
        self.attribute2 = attribute2 #initial value for attribute2 passed
        # ...

	# Defining methods
	def function_name(self, param1, param2,...):
		# body of function

4. Constructing an Instance of the Object

Create instances (objects) of the class by calling the class as if it were a function. This creates the class object stored in the variable in which it is assigned to:

obj_name = ClassName(0)

The variable essentially points to the template in memory (created via class keyword) and is used to access the code and data for that particular instance of the class .

Accessing Attributes and Invoking Methods

To invoke a method of the class, we use the dot notation to call the method for that object as defined in the class:

obj_name.method()

Use dot notation to access attributes:

obj_name.attribute1