creating_classes.md

Creating Classes

Syntax for Class Definition

In Python, a class is defined using the class keyword, followed by the class name and a colon. The class name typically follows the CapWords convention. Here’s a basic example:

class Car:
    # class body

Class Attributes and Methods

• Class Attributes: These are variables that are shared by all instances of a class. They are defined within the class but outside of any methods. Class attributes are used for data that is common to all instances.

class Car:
    wheels = 4  # Class attribute

• Class Methods: Methods are functions defined within the class. They describe the behaviors that instances of the class can perform.

class Car:
    def start_engine(self):
        print("Engine started")

The __init__ Method (Constructor)

The __init__ method in Python is a special method that is automatically called when a new instance of a class is created. It is used to initialize the instance.

• self Parameter: The first parameter of __init__ (and typically all instance methods) is self, which refers to the instance being created.

class Car:
    def __init__(self, make, model):
        self.make = make
        self.model = model

Creating an Instance of a Class

To create an instance of a class, you simply call the class as if it were a function, passing the arguments that its __init__ method expect

my_car = Car("Toyota", "Corolla")

Instance Variables vs. Class Variables

• Instance Variables: These are variables that are unique to each instance of a class. They are typically defined within methods, using the self parameter. Each instance has its own copy of instance variables.

class Car:
    def __init__(self, make, model):
        self.make = make  # Instance variable
        self.model = model  # Instance variable

• Class Variables: In contrast, class variables are shared by all instances of the class. They are defined at the class level, outside of any methods.

class Car:
    wheels = 4  # Class variable

    def __init__(self, make, model):
        self.make = make
        self.model = model

Creating Methods in a Class

Methods in a class need the self parameter to access and modify the instance's attributes.
self refers to the current instance of the class.

class Car:
    # ...

    def display_info(self):
        """Prints information about the car."""
        print(f"This is a {self.make} {self.model}.")s

Attributes of an instance can be accessed and modified using the dot notation. This is done using the self keyword within class methods.

class Car:
    # ...

    def update_model(self, new_model):
        """Updates the car's model."""
        self.model = new_model

Documentation

In Python, documenting a class is done using docstrings, which are multiline strings enclosed in triple quotes. Docstrings provide a convenient way of associating documentation with Python code.

class Car:
    """
    Class representing a car.

    Attributes:
        wheels (int): Number of wheels the car has.
        make (str): The manufacturer of the car.
        model (str): The model of the car.
    """

    wheels = 4

    def __init__(self, make, model):
        """
        Initialize a new Car instance.

        Parameters:
            make (str): The manufacturer of the car.
            model (str): The model of the car.
        """
        self.make = make
        self.model = model

References

• PythonDocs
• RealPython