Question 475 of 169
Method Resolution Order (MRO) in Multiple Inheritance
A class inherits from two parent classes that both have a method with the same name. When calling the method on the child, only one parent's version is executed. What Python mechanism determines which one?
Quick Answer
The answer is the Method Resolution Order (MRO), which Python uses to determine which parent class method is executed in a multiple inheritance scenario. This is correct because Python applies the C3 linearization algorithm to compute a consistent, left-to-right search order through the inheritance hierarchy; when a method is called on a child instance, Python walks the MRO and executes the first matching implementation it encounters, ensuring predictable behavior even in complex diamond patterns. On the Certified Associate Python Programmer PCAP exam, this concept tests your understanding of how Python resolves method conflicts in multiple inheritance, often appearing in questions where two parent classes define the same method name—a common trap is assuming the child must override the method or that Python uses depth-first search. To remember the rule, think "MRO: leftmost parent wins first, then up the chain," or use the mnemonic "My Rightful Order" to recall that the order is computed, not guessed.
⚠ Common exam trap
Python Institute often tests the misconception that Python uses 'closest parent wins' or depth-first search, but the actual mechanism is the C3 linearization MRO, which respects base class order and the diamond inheritance pattern.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Method Resolution Order (MRO).
Python uses the C3 linearization algorithm to compute the Method Resolution Order (MRO) for a class. When a method is called on an instance, Python searches the MRO from left to right and executes the first implementation it finds. This ensures a consistent and predictable order of inheritance, even in diamond or multiple-inheritance scenarios.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Method overloading by signature.
Why it's wrong here
Python does not support method overloading.
- ✗
Explicit super() call in the child class.
Why it's wrong here
super() is used to call parent methods, but it follows MRO.
- ✗
Inheritance depth (closest parent wins).
Why it's wrong here
MRO considers multiple factors, not just depth.
- ✓
Method Resolution Order (MRO).
Why this is correct
MRO determines the order of method lookup in multiple inheritance.
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Same concept, more angles
1 more way this is tested on PCAP
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A developer creates classes `A`, `B(A)`, `C(A)`, and `D(B, C)`. When calling a method from `D` that is defined in `A`, which class's version is used according to Python's MRO?
medium- A.The method from B, because it is the first parent.
- B.The method from C, because it appears after B.
- C.The method from A, but only if B and C do not override it.
- ✓ D.The method from A, found through B then C.
Why D: Python's Method Resolution Order (MRO) for class `D(B, C)` follows the C3 linearization algorithm, which ensures a depth-first left-to-right search while preserving monotonicity. For `D(B, C)`, the MRO is `D -> B -> C -> A`, so a method defined in `A` that is not overridden in `B` or `C` will be found via `B` first, then `C`, and finally `A`. Option D correctly states that the method from `A` is used, found through `B` then `C`, which matches the actual resolution path.
Last reviewed: Jun 30, 2026
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