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Inheritance

Multiple Inheritance

Inheriting from multiple parent classes and the diamond problem

Interview: Advanced OOP — tests understanding of MRO, diamond problem, and when multiple inheritance is appropriate

Last Updated: June 12, 2026 • 7 min read

Multiple inheritance allows a class to inherit from more than one parent class. While powerful, it introduces complexity like the diamond problem. Python resolves method conflicts using the C3 linearization algorithm (MRO). Use multiple inheritance carefully — mixins are the safest use case.

The Diamond Problem

When two parent classes share a common ancestor, and the child inherits from both parents, which ancestor method should be called? Python's MRO resolves this using C3 linearization, ensuring a consistent, predictable order.

Best Practices

  • Use mixins — small, focused classes that add specific functionality
  • Keep inheritance hierarchies shallow
  • Always use super() to call parent methods (ensures MRO is followed)
  • Avoid inheriting from classes that weren't designed for multiple inheritance
  • Consider composition or protocols as alternatives

Common Pitfall

The order of parent classes matters! class D(B, C) is different from class D(C, B). Python searches left to right, so B's methods take precedence over C's.

Use Cases

Adding serialization (JSON, XML) to any class via mixins

Logging capabilities across unrelated class hierarchies

GUI frameworks: combining draggable, resizable, closable behaviors

Django class-based views: LoginRequiredMixin, PermissionRequiredMixin

Adding comparison behavior (ComparableMixin) to custom classes

Common Mistakes

Inheriting from parents in wrong order — affects method resolution

Creating complex diamond hierarchies that are hard to reason about

Not using super() in all methods — breaks MRO chain

Using multiple inheritance when composition would be simpler

Mixins that depend on methods/attributes not guaranteed to exist