What are classes and objects in Python?

A class is a template (blueprint) for creating objects. An object is a specific instance of a class.

Defining a class:

class Dog:
    # Class attribute (shared by all instances)
    species = "Canis familiaris"

    # Constructor — gets called when creating an object
    def __init__(self, name, age):
        # Instance attributes (unique to each object)
        self.name = name
        self.age = age

    # Instance method
    def bark(self):
        return f"{self.name} says: Woof!"

Creating objects:

dog1 = Dog("Bobik", 3)
dog2 = Dog("Sharik", 5)

print(dog1.name)      # Bobik
print(dog2.bark())    # Sharik says: Woof!
print(dog1.species)   # Canis familiaris

self:

• self is a reference to the current instance of the class.
• It is passed automatically when a method is called.
• Through self, you can access the object's attributes and methods.

Class attributes vs instance attributes:

class Counter:
    count = 0  # Class attribute — shared by all

    def __init__(self):
        Counter.count += 1  # Modify the class attribute
        self.id = Counter.count  # Instance attribute

c1 = Counter()
c2 = Counter()
print(Counter.count)  # 2
print(c1.id, c2.id)   # 1 2