How to Construct Classes and Define Objects in Python 3 – Complete Guide 2025–2026

February 8, 2026
Tutorial Series
Comment off

Learning how to construct classes and define objects in Python 3 is one of the most powerful and frequently used skills at Progressive Robot. Constructing classes and defining objects in Python 3 forms the foundation of object-oriented programming (OOP), allowing you to create reusable blueprints (classes) and concrete instances (objects) that model real-world entities, encapsulate data and behaviour, promote code reuse, improve maintainability, and build scalable applications — from simple scripts to enterprise systems, web APIs, data pipelines, games, and AI models.

In this up-to-date 2025–2026 Progressive Robot guide, you’ll master exactly how to construct classes and define objects in Python 3: class syntax, __init__ constructor method, self parameter, instance vs class attributes, methods, creating multiple objects, inheritance basics, best practices, and real-world patterns. All examples are tested on Python 3.10–3.13.

Key Takeaways – How to Construct Classes and Define Objects in Python 3

Construct classes in Python 3 using class ClassName: — this creates a blueprint for objects.
Define objects (instances) from a class with obj = ClassName(args).
__init__(self, …) is the constructor method — automatically runs when you construct classes and define objects in Python 3 to initialize attributes.
self always refers to the current instance — required in every instance method when defining objects in Python 3.
Instance attributes (via self.) are unique per object; class attributes are shared across all objects.
You can construct classes and define objects in Python 3 with multiple instances — each behaves independently.
Use docstrings and type hints for professional, maintainable code when constructing classes and defining objects in Python 3.

Prerequisites

Python 3.8+ installed (Progressive Robot recommends 3.12+)
Basic Python knowledge (functions, variables, print)
Interactive shell (python3) or script file

1. Basic Class Definition – First Step to Construct Classes in Python 3

				
					class Shark:
    """Blueprint for shark objects."""
    
    def swim(self):
        print("The shark is swimming.")
    
    def be_awesome(self):
        print("The shark is being awesome.")

This is how you construct classes in Python 3 — a blueprint is created, but no objects exist yet.

2. Defining (Instantiating) Objects

				
					sammy = Shark()  # Create object (instance) of Shark class
sammy.swim()     # The shark is swimming.
sammy.be_awesome()  # The shark is being awesome.

Each object (sammy) is independent — you can create many:

				
					stevie = Shark()
stevie.swim()  # Another shark swimming

The init Constructor Method – Core When Constructing Classes in Python 3

__init__ runs automatically when an object is created — perfect for initialization.

				
					class Shark:
    def __init__(self, name: str):
        self.name = name  # instance attribute
    
    def swim(self):
        print(f"{self.name} is swimming.")
    
    def be_awesome(self):
        print(f"{self.name} is being awesome.")

Now create objects with data:

				
					sammy = Shark("Sammy")
sammy.swim()      # Sammy is swimming.
sammy.be_awesome()  # Sammy is being awesome.

stevie = Shark("Stevie")
stevie.swim()     # Stevie is swimming.

4. Class vs Instance Attributes When Defining Objects in Python 3

				
					class Shark:
    species = "shark"  # class attribute – shared by all objects
    
    def __init__(self, name: str, age: int):
        self.name = name   # instance attribute – unique per object
        self.age = age

sammy = Shark("Sammy", 5)
stevie = Shark("Stevie", 3)

print(sammy.species)   # shark (class attr)
print(stevie.species)  # shark (same)
print(sammy.name)      # Sammy (instance attr)
print(stevie.name)     # Stevie (different)

5. Full Example – Constructing Classes and Defining Objects in Python 3

				
					class Shark:
    """Blueprint for shark objects at Progressive Robot."""
    
    def __init__(self, name: str, age: int, color: str = "grey"):
        self.name = name
        self.age = age
        self.color = color
    
    def swim(self) -> None:
        """Make the shark swim."""
        print(f"{self.name} ({self.color}) is swimming.")
    
    def birthday(self) -> None:
        """Increase age by 1."""
        self.age += 1
        print(f"Happy birthday! {self.name} is now {self.age} years old.")

def main():
    sammy = Shark("Sammy", 5, "blue")
    stevie = Shark("Stevie", 3)
    
    sammy.swim()      # Sammy (blue) is swimming.
    stevie.swim()     # Stevie (grey) is swimming.
    
    sammy.birthday()  # Happy birthday! Sammy is now 6 years old.

if __name__ == "__main__":
    main()

6. Best Practices & Modern Tips (2025–2026 – Progressive Robot Style)

Always use self as first parameter in instance methods.
Add docstrings to class and every method (Google or NumPy style).
Use type hints: def swim(self) -> None: — improves readability & IDE support.
Keep __init__ simple — move complex setup to other methods.
Use class attributes for shared constants (e.g., species = “shark”).
Prefer composition over deep inheritance.
Use @property for getter/setter logic when needed.

How to Construct Classes and Define Objects in Python 3 – FAQ (2025–2026)

How do I construct classes in Python 3?
Use class ClassName: — blueprint for objects — basic way to construct classes in Python 3.
How do I define objects from a class in Python 3?
obj = ClassName(args) — creates instance (object).
What does init do when defining classes in Python 3?
Constructor method — runs automatically on object creation to initialize attributes.
What is self in Python 3 classes?
Reference to the current instance — required in every instance method.
How do I create multiple objects of the same class in Python 3?
Just call the class multiple times: obj1 = ClassName(), obj2 = ClassName() — each is independent.

Summary

You now know exactly how to construct classes and define objects in Python 3: class syntax, __init__ constructor, self parameter, instance/class attributes, methods, creating multiple objects, and Progressive Robot best practices.

Mastering how to construct classes and define objects in Python 3 unlocks true OOP power — reusable blueprints, encapsulated data/behaviour, scalable design — essential for building clean, maintainable applications at Progressive Robot.