What are Classes & Objects?

01 What is a Class?

In crisp, formal engineering terms:

Before an architectural firm erects a modern skyscraper, architects draft an exact blueprint detailing the dimensions, materials, and structural load pathways. In the exact same way, before creating living objects in software, we define a Class.

02 Then What is an Object?

If the Class is the blueprint, then:

When the language runtime allocates heap memory according to the class specification and assigns distinct attribute values, an Object is born.

Notice: All three students originate from the identical Student class specification. Every one of them has fields for name, age, and ID. Yet each individual object manages its own private, isolated state.

03 A Classic Real-World Analogy: The House Blueprint

To permanently crystallize this mental model, consider residential architecture:

04 The Anatomy of an Object: Identity, State, and Behavior

In computer science, any true object is rigorously characterized by three fundamental dimensions:

05 Working Code Walkthrough in Python

Let us observe how classes are formally defined and instantiated using modern Python syntax:

# 1. Define the Class Blueprint
class Student:
    # Constructor: invoked automatically when instantiating a new object
    def __init__(self, name, student_id, major):
        self.name = name              # Instance attribute (State)
        self.student_id = student_id  # Unique identifier
        self.major = major            # Academic department
        self.enrolled_courses = []    # Initial dynamic state

    # Defined Behavior (Method)
    def enroll(self, course_name):
        self.enrolled_courses.append(course_name)
        print(f"[{self.name}] successfully enrolled in '{course_name}'.")

    def introduce(self):
        print(f"Hello, I am {self.name} (ID: {self.student_id}), majoring in {self.major}.")

# 2. Instantiate Living Objects from the Blueprint
s1 = Student("Rahim", 101, "Computer Science")
s2 = Student("Karim", 102, "Data Engineering")

# 3. Invoke Methods and Observe State Mutability
s1.introduce()  # Output: Hello, I am Rahim (ID: 101), majoring in Computer Science.
s2.introduce()  # Output: Hello, I am Karim (ID: 102), majoring in Data Engineering.

s1.enroll("Algorithms 101")
print(s1.enrolled_courses)  # ['Algorithms 101']
print(s2.enrolled_courses)  # [] — Karim's state remains completely untouched!

Observe three fundamental mechanics:

• class Student: specifies the shape and capabilities of all students.
• s1 = Student(...) creates an independent instance with its own memory allocation.
• When invoking s1.enroll(), only s1's internal course list mutates. s2 remains completely isolated.

06 Verifying Memory & Identity: id() and the is Operator

A common conceptual question arises: "If two distinct objects hold identical data in every field, are they the same object?"

The answer is an unequivocal No. Let us verify this directly in Python:

student_a = Student("Ayesha", 500, "Math")
student_b = Student("Ayesha", 500, "Math")

# Do they hold equal data values?
print(student_a.name == student_b.name)  # True

# Are they the same physical instance in memory?
print(student_a is student_b)            # False!

# Inspect their discrete memory addresses:
print(hex(id(student_a)))                # e.g., 0x7f9a2b8c41f0
print(hex(id(student_b)))                # e.g., 0x7f9a2b8c4d90 (Discrete memory cells!)

07 Are Classes Only for Physical Real-World Entities?

Beginners often assume classes can only represent tangible physical objects you can touch with your hands (such as cars, dogs, books, or people).

In production software engineering, the vast majority of classes actually model abstract conceptual and architectural components:

A PaymentGateway has no physical embodiment in the real world. However, it holds vital state (API credentials, active session tokens) and executes mission-critical behavior (charge_card(), refund()). Therefore, it is an exemplary object.

08 Quick Mental Anchor: Recipe vs. The Cooked Meal

Whenever you need an instantaneous, foolproof heuristic to differentiate Class and Object, recall the culinary world: