🐍Python Programming
OOP in Python
Classes, objects, inheritance, polymorphism, dunder methods, and properties.
BeginnerIntermediateAdvanced
What You Will Learn in OOP in Python
Python OOP allows defining classes as blueprints for objects with attributes and methods, supporting inheritance, encapsulation, and polymorphism.
- `__init__` is Python's constructor; `self` refers to the current instance.
- Name mangling: `__attr` makes attribute private (not truly, but harder to access externally).
- Inheritance: `class Child(Parent)` — `super()` calls parent's methods.
- Dunder (magic) methods: `__str__`, `__repr__`, `__len__`, `__add__` enable operator overloading.
- @property decorator: define computed attributes accessed like attributes (not methods).
- Multiple inheritance supported; MRO (Method Resolution Order) follows C3 linearisation.
Syntax
class ClassName(ParentClass):
class_var = value # class variable (shared)
def __init__(self, args):
self.instance_var = args # instance variable
def method(self):
return self.instance_var
def __str__(self): # string representation
return f"ClassName({self.instance_var})"Complete Code Example
class BankAccount:
interest_rate = 0.05 # class variable
def __init__(self, owner, balance=0):
self.owner = owner
self.__balance = balance # private
@property
def balance(self): return self.__balance
def deposit(self, amount):
if amount > 0: self.__balance += amount
def __str__(self):
return f"Account({self.owner}, ₹{self.__balance})"
class SavingsAccount(BankAccount):
def add_interest(self):
self.deposit(self.balance * BankAccount.interest_rate)
acc = SavingsAccount("Priya", 10000)
acc.add_interest()
print(acc) # Account(Priya, ₹10500.0)Example
A `Student` class with `__init__(name, roll)` creates student objects with unique attributes.
Expected Exam Questions — OOP in Python
Q1.What is `self` in Python? Is it mandatory?
Answer: `self` refers to the current instance of the class. It must be the first parameter of all instance methods. The name `self` is a convention (not a keyword) — you could use any name, but `self` is universally used.
Q2.Explain method resolution order (MRO) in Python's multiple inheritance.
Answer: MRO determines the order in which base classes are searched for a method. Python uses C3 linearisation. Check with `ClassName.__mro__`. Generally: class itself → left parent → right parent → common ancestors. The `super()` function follows MRO.
Q3.What are `__str__` and `__repr__`? When are they called?
Answer: `__str__` returns a human-readable string, called by `print()` and `str()`. `__repr__` returns an unambiguous developer-friendly representation, called by `repr()` and in the REPL. If `__str__` is missing, Python falls back to `__repr__`.
🔘 MCQ Practice — OOP in Python
MCQ 1.What does `@property` decorator do in Python?
A. Makes a method a class method
B. Allows a method to be accessed as an attribute ✓
C. Makes an attribute private
D. Converts a method to a static method
✓ Correct Answer: Allows a method to be accessed as an attribute
MCQ 2.In Python, how do you call a parent class method from a child class?
A. parent.method()
B. base.method()
C. super().method() ✓
D. this.method()
✓ Correct Answer: super().method()
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