README.md

Inheritance & MRO

Method Resolution Order determines which parent class method Python calls in multiple inheritance.

Files

File	Description
example.py	Diamond inheritance, super(), Duck mixin

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Descriptive Example

Scenario

Classic diamond: D inherits from B and C, both inherit from A. What order does Python search?

class A:
    def greet(self):
        return "A"

class B(A):
    def greet(self):
        return f"B -> {super().greet()}"

class C(A):
    def greet(self):
        return f"C -> {super().greet()}"

class D(B, C):
    def greet(self):
        return f"D -> {super().greet()}"

print(D.__mro__)
# (<class 'D'>, <class 'B'>, <class 'C'>, <class 'A'>, <class 'object'>)

print(D().greet())   # D -> B -> C -> A

super() follows MRO — it does not simply call the direct parent class.

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Interview Q&A

Q1: What is MRO?
A: Method Resolution Order — the linear order Python searches base classes for attributes/methods. Computed via C3 linearization algorithm.

Q2: What is the diamond problem?
A: When two parent classes share a grandparent, which grandparent.method() gets called? Python's MRO resolves this deterministically.

Q3: Does super() call the parent class?
A: No. It calls the next class in the MRO after the current class. In D(B,C), super() in B calls C, not necessarily A directly.

Q4: How do you inspect MRO?
A: ClassName.__mro__ or ClassName.mro().

Q5: What is a mixin?
A: A class providing behavior but not meant to stand alone. Mixed into inheritance for reusable features (e.g., JsonMixin, TimestampMixin).

Q6: Multiple inheritance vs composition?
A: Inheritance: "is-a" relationship. Composition: "has-a" — often preferred for flexibility. Favor composition when inheritance hierarchies get deep.

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Run

python3 example.py