Method Resolution Order (MRO)

What this problem practises

Object-oriented bugs hide in state: class attributes shared by every instance, mutable defaults declared in __init__ signatures, and methods that mutate self when the caller expected a copy.

This is an output-prediction problem: read the snippet carefully and write down exactly what it prints before anything runs. These questions are interview staples because they test whether you know the language rules, or merely recognise their syntax.

Difficulty: hard — the naive reading is wrong, and the answer depends on tracking state precisely through the snippet.

The challenge

This is a premium problem. Premium unlocks the complete catalog and an ad-free editor; every hint on every problem is free for all learners.

Keep going

• Output-prediction strategies — how to predict tricky snippets without running them.
• Browse every oop problem in this topic.
• Common Python errors and what they actually mean, plus the Python glossary for any term used on this page.