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.
Consider the following class hierarchy: class A: def method(self): return 'A'; class B(A): pass; class C(A): def method(self): return 'C'; class D(B, C): pass. What is the output of D().method() according to Python's MRO?
'B'
Why wrong: B does not override method().
TypeError
Why wrong: No error; method resolution succeeds.
'A'
Why wrong: A is not the first class with method() in MRO.
'C'
C's method() is found first in the MRO.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
'C'
Python's MRO (Method Resolution Order) for class D(B, C) is computed using the C3 linearization algorithm, which respects the local precedence order and monotonicity. The MRO for D is D -> B -> C -> A, so D().method() resolves to C.method(), returning 'C'. Option D is correct because C is the first class in the MRO that defines method().
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
'B'
Why it's wrong here
B does not override method().
TypeError
Why it's wrong here
No error; method resolution succeeds.
'A'
Why it's wrong here
A is not the first class with method() in MRO.
'C'
Why this is correct
C's method() is found first in the MRO.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Python Institute often tests the C3 linearization rule that the MRO respects the order of base classes in the class definition, so candidates mistakenly think B's inheritance from A takes precedence over C's override, leading them to pick 'A' or 'B' instead of 'C'.
Detailed technical explanation
The C3 linearization algorithm ensures a consistent MRO by merging the linearizations of parent classes while preserving the order of appearance in the class definition. In this diamond inheritance pattern, the MRO is D -> B -> C -> A, which avoids the 'diamond problem' by prioritizing the most specific override (C) over the common ancestor (A). Understanding MRO is critical when designing mixins or frameworks that rely on cooperative multiple inheritance, such as Django's class-based views.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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FAQ
Object-Oriented Programming — This question tests Object-Oriented Programming — Read the scenario before looking for a memorised answer..
The correct answer is: 'C' — Python's MRO (Method Resolution Order) for class D(B, C) is computed using the C3 linearization algorithm, which respects the local precedence order and monotonicity. The MRO for D is D -> B -> C -> A, so D().method() resolves to C.method(), returning 'C'. Option D is correct because C is the first class in the MRO that defines method().
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This PCAP practice question is part of Courseiva's free Python Institute certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCAP exam.
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