The answer is that the base classes were listed in the wrong order in the class definition. Python's Method Resolution Order (MRO) uses the C3 linearization algorithm, which determines method lookup by scanning base classes from left to right as they appear in the class header. When you write class C(A, B), the MRO becomes C → A → B, so A's method is found first; but if you write C(B, A), the MRO reverses to C → B → A, causing B's method to take precedence. On the PCAP exam, this tests your understanding of multiple inheritance and the MRO, often appearing as a trick where the developer’s expectation contradicts the declared order. A common trap is assuming inheritance hierarchy alone dictates method resolution, when in fact the left-to-right order in the class definition is decisive. Remember the mnemonic: “Left is first” — the class you list first in parentheses gets priority in the MRO.
PCAP Object-Oriented Programming Practice Question
This PCAP practice question tests your understanding of object-oriented programming. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A Python program uses multiple inheritance. Class A defines method 'foo', class B also defines 'foo', and class C(A, B) inherits from both. The developer expects that calling 'foo' on an instance of C should invoke the method from class A. However, it invokes the method from class B. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The method resolution order (MRO) is not as expected due to the order of base classes
Option A is correct because Python's Method Resolution Order (MRO) uses the C3 linearization algorithm, which respects the order of base classes as listed in the class definition. When class C(A, B) is defined, the MRO is C → A → B, so 'foo' from A should be found first. However, if the developer mistakenly wrote C(B, A), the MRO becomes C → B → A, causing B's 'foo' to be invoked. The question states the developer expected A's method but got B's, indicating the base class order was reversed.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
The method resolution order (MRO) is not as expected due to the order of base classes
Why this is correct
MRO uses C3 linearization; if B's method is called, the MRO likely lists B before A, possibly due to a different inheritance structure.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Python always calls the method from the last base class
Why it's wrong here
Python uses C3 linearization, not a simple last-base rule.
✗
The 'foo' method in class B is defined after class A's 'foo' in the same file
Why it's wrong here
Definition order in the file does not affect MRO.
✗
Python uses depth-first, left-to-right resolution
Why it's wrong here
Python uses C3 linearization, not depth-first.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the misconception that Python uses simple depth-first, left-to-right resolution (like some older languages), when in fact it uses the C3 linearization algorithm, and the order of base classes in the class definition is the primary factor determining which method is called.
Detailed technical explanation
How to think about this question
The C3 linearization algorithm, introduced in Python 2.3, computes the MRO by merging the linearizations of parent classes while preserving local precedence order and monotonicity. This ensures that if class C inherits from A and B, the MRO respects the order C, A, B (if C(A, B)) or C, B, A (if C(B, A)). A real-world scenario where this matters is when using mixins: placing a mixin before a base class can override methods unintentionally if the developer does not understand MRO.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Object-Oriented Programming — This question tests Object-Oriented Programming — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The method resolution order (MRO) is not as expected due to the order of base classes — Option A is correct because Python's Method Resolution Order (MRO) uses the C3 linearization algorithm, which respects the order of base classes as listed in the class definition. When class C(A, B) is defined, the MRO is C → A → B, so 'foo' from A should be found first. However, if the developer mistakenly wrote C(B, A), the MRO becomes C → B → A, causing B's 'foo' to be invoked. The question states the developer expected A's method but got B's, indicating the base class order was reversed.
What should I do if I get this PCAP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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