`super()` — calling parent methods

2.1.9 · Coding › OOP Fundamentals

super() KYA hai?

Toh iske bajaay:

class Dog(Animal):
    def __init__(self, name):
        Animal.__init__(self, name)   # hard-coded parent name

tum likhte ho:

class Dog(Animal):
    def __init__(self, name):
        super().__init__(name)        # decoupled from parent name

YEH kyun exist karta hai? (woh problem jo yeh solve karta hai)

YEH kaise kaam karta hai — first principles se derive kiya hua

Koi magic nahi hai. super() bas Parent.method(self) hi hai lekin parent ko dynamically MRO ke through choose kiya jaata hai.

Step 1 — har class ka ek MRO hota hai. Python ek linear order of classes compute karta hai kisi attribute ko search karne ke liye. Ise dekho:

Dog.__mro__   # (Dog, Animal, object)

Step 2 — class C ke method ke andar super() ka matlab hai:

"type(self) ke MRO mein C ke baad wali position se search shuru karo, aur self bind karo."

Step 3 — equivalence derive karo. Dog.__init__ ke andar, super() conceptually yeh hai: $\text{super()}\equiv \text{super(Dog, self)}$ jo type(self).__mro__ mein Dog ke baad wali class (yahan Animal) dhoondta hai aur uska method self ke saath call karta hai jo pehle se supplied hai. Isliye tum super().__init__(name) likhte ho aur nahi super().__init__(self, name) — self automatically inject ho jaata hai.

Worked Example 1 — __init__ extend karna

class Animal:
    def __init__(self, name):
        self.name = name
        self.legs = 4
 
class Dog(Animal):
    def __init__(self, name, breed):
        super().__init__(name)   # parent sets name + legs
        self.breed = breed       # child adds extra state
 
d = Dog("Rex", "Lab")
print(d.name, d.legs, d.breed)   # Rex 4 Lab

• super().__init__(name) pehle kyun? Taaki self.name aur self.legs child ke apne attributes add karne se pehle exist karein — child extend karta hai, replace nahi karta.
• self kyun nahi? Proxy ne already self bind kar liya hai; dobara pass karne par "got multiple values for argument" error aata hai.

Worked Example 2 — ek normal method extend karna

class Logger:
    def save(self, data):
        print("validating", data)
        return True
 
class TimestampLogger(Logger):
    def save(self, data):
        ok = super().save(data)      # reuse parent's validation
        print("saved at 12:00", data)
        return ok

• Validation copy karne ki jagah super().save kyun call karte hain? Agar Logger mein validation logic change ho, to child automatically sahi rehta hai (single source of truth).

Worked Example 3 — multiple inheritance aur MRO

class A:
    def __init__(self): print("A"); super().__init__()
class B(A):
    def __init__(self): print("B"); super().__init__()
class C(A):
    def __init__(self): print("C"); super().__init__()
class D(B, C):
    def __init__(self): print("D"); super().__init__()
 
D()                 # prints D B C A  (each ONCE)
print([c.__name__ for c in D.__mro__])  # D B C A object

• D B C A kyun aur D B A C A kyun nahi? Kyunki B mein super() ka matlab "go to A" nahi hai — iska matlab hai "D ke MRO mein next class pe jao," jo C hai. MRO guarantee karta hai ki A exactly ek baar run ho. Yeh woh killer feature hai jo tum A.__init__(self) se nahi paa sakte.

Flashcards

Connections

• Inheritance — extending classes
• Method Resolution Order (MRO) & C3 Linearization
• Method Overriding vs Overloading
• Multiple Inheritance & the Diamond Problem
• `__init__` — constructors
• Composition over Inheritance

Concept Map