Here’s a complete OOP interview questions set for Python — from basic to advanced — with ✅ real-world relevance, 🧠 conceptual focus, and 🧪 coding triggers. You can practice or review these inline (Notion/blog-style ready).

🧠 Python OOP Interview Questions (With Hints)

🔹 Basic Level (Conceptual Clarity)

1. What is the difference between a class and an object?

🔸 Hint: Think of blueprint vs instance.

2. What is `self` in Python classes?

🔸 Hint: Refers to the instance calling the method.

3. What does the `init()` method do?

🔸 Hint: Think constructor/initializer.

4. How is `@staticmethod` different from `@classmethod`?

🔸 Hint: Focus on parameters (self, cls, none).

5. What is encapsulation and how is it implemented in Python?

🔸 Hint: Using _protected or __private attributes.

🔹 Intermediate Level (Design + Usage)

6. What is inheritance and how is it used in Python?

🔸 Hint: class Dog(Animal) → Dog inherits from Animal.

7. What is multiple inheritance? Any issues with it?

🔸 Hint: Method Resolution Order (MRO) and super().

8. Explain polymorphism with an example.

🔸 Hint: Same method name, different behavior in subclasses.

9. What is the difference between overloading and overriding?

🔸 Hint: Overloading = same method with different args (limited in Python); Overriding = subclass changes parent behavior.

10. What is composition in OOP? How is it better than inheritance sometimes?

🔸 Hint: “Has-a” relationship. Flexible over tight coupling.

🔹 Advanced Level (Dunder + Architecture)

11. What are dunder methods? Why are they useful?

🔸 Hint: __str__, __len__, __eq__, __getitem__, etc.

12. What does the `call()` method do?

🔸 Hint: Allows object to be used like a function.

13. What’s the difference between `str` and `repr`?

🔸 Hint: str is readable, repr is for debugging (dev-facing).

14. How can you make a class iterable?

🔸 Hint: Implement __iter__() and __next__().

15. How do you implement abstraction in Python?

🔸 Hint: Use abc.ABC and @abstractmethod.

🔹 Real-World + Design Questions

16. How would you design a logging system using OOP?

🔸 Hint: Use base Logger class and subclasses for FileLogger, DBLogger.

17. What design patterns use inheritance or composition?

🔸 Hint: Inheritance → Template, Strategy; Composition → Decorator, Adapter.

18. When should you prefer composition over inheritance?

🔸 Hint: When you want flexibility and loose coupling.

19. How do you protect class attributes from being modified directly?

🔸 Hint: Use @property, private variables (__balance), setters.

20. What are `dataclasses` in Python? How do they help?

🔸 Hint: Auto-generate boilerplate code (__init__, __repr__, etc.).

🔹 Practical Coding Prompts

🧪 Q21. Write a class `BankAccount` with deposit, withdraw, and balance check. Use private attributes.

🧪 Q22. Write a base class `Shape` and subclasses like `Circle`, `Rectangle` with their own `area()` methods.

🧪 Q23. Create a `Car` class that has an `Engine` object using composition. Call `engine.start()` from car.

🧪 Q24. Create a `Logger` base class. Create `FileLogger` and `ConsoleLogger` subclasses using polymorphism.

🧪 Q25. Implement a class where calling the object increments a counter (`call()`).

📘 Bonus: Quick Tips

✅ @classmethod → Used for alternate constructors (from_json, from_dict)
✅ @staticmethod → Pure functions that belong to a class for grouping
✅ Prefer composition when behavior needs to be reused rather than extended
✅ Use super() to call parent methods in child class overrides

Absolutely! Here’s your inline sample answer key to the 25 Python OOP interview questions above — clean, short, and suitable for review, Notion, or blog use.

📝 Python OOP Interview – Sample Answer Key

🔹 Basic Level

1. Class vs Object

Class: A blueprint for creating objects.
Object: An instance of a class with actual data.

2. What is `self`?

Refers to the current instance of the class.
Used to access instance variables and methods.

3. What is `init()`?

The constructor method called when an object is created.
Initializes object attributes.

4. `@staticmethod` vs `@classmethod`

@staticmethod: No self or cls, behaves like a regular function inside class.
@classmethod: Receives cls, can access/modify class state.

5. Encapsulation

Hides internal data using _protected or __private variables.
Achieved via access modifiers and getter/setter methods.

🔹 Intermediate Level

6. Inheritance

One class inherits methods/attributes from another.
Promotes code reuse.

class Dog(Animal):
    pass

7. Multiple Inheritance & MRO

A class inherits from multiple parent classes.
Python resolves method conflicts using MRO (Method Resolution Order).

class A: pass
class B: pass
class C(A, B): pass

8. Polymorphism

Multiple classes have methods with the same name but different behaviors.

def speak(animal): animal.speak()

9. Overloading vs Overriding

Overriding: Subclass redefines parent method.
Overloading: Not natively supported; achieved with default args or *args.

10. Composition

One class uses another class inside it (HAS-A).
Preferred over inheritance for flexibility.

class Car:
    def __init__(self):
        self.engine = Engine()

🔹 Advanced Level

11. Dunder Methods

Special methods with __ prefix/suffix (e.g., __init__, __str__).
Define object behavior in built-in operations.

12. `call()`

Makes object behave like a function.

class Counter:
    def __call__(self): ...

13. `str` vs `repr`

__str__: Human-readable (print)
__repr__: Debug/developer-friendly

14. Iterable Object

class MyList:
    def __iter__(self): ...
    def __next__(self): ...

15. Abstraction

Hide implementation using abstract base class:

from abc import ABC, abstractmethod
class Shape(ABC):
    @abstractmethod
    def area(self): pass

🔹 Real-World + Design

16. Logger System

class Logger: ...
class FileLogger(Logger): ...
class DBLogger(Logger): ...

17. Design Patterns

Inheritance: Strategy, Template
Composition: Adapter, Decorator

18. Composition > Inheritance

Use composition when behaviors are modular and interchangeable.

19. Protecting Attributes

class User:
    def __init__(self): self.__age = 0
    def get_age(self): return self.__age

20. Dataclasses

from dataclasses import dataclass
@dataclass
class Point:
    x: int
    y: int

🔹 Coding Practice Questions (Samples)

21. BankAccount Class

class BankAccount:
    def __init__(self):
        self.__balance = 0

    def deposit(self, amt): self.__balance += amt
    def get_balance(self): return self.__balance

22. Shape → Circle, Rectangle

class Shape(ABC):
    @abstractmethod
    def area(self): pass

class Circle(Shape):
    def area(self): return 3.14 * 5 * 5

23. Car-Engine Composition

class Engine:
    def start(self): print("Engine on")

class Car:
    def __init__(self): self.engine = Engine()
    def drive(self): self.engine.start()

24. Logger Polymorphism

class Logger:
    def log(self, msg): pass

class FileLogger(Logger):
    def log(self, msg): print("File:", msg)

25. `call()` Example

class Counter:
    def __init__(self): self.count = 0
    def __call__(self): self.count += 1; return self.count

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Complete OOP interview questions set for Python — from basic to advanced