Quick Answer
The correct answer is composition over inheritance. This principle is the right choice because it structures the `Car` class to contain `Engine` and `Transmission` objects as attributes, forming flexible "has-a" relationships instead of rigid "is-a" hierarchies. By favoring composition, you avoid deep inheritance chains that become brittle and hard to maintain, allowing you to swap or modify components at runtime without breaking the entire system. On the Certified Associate Python Programmer PCAP exam, this concept tests your understanding of object-oriented design best practices, often appearing in scenario-based questions where a deep hierarchy would be impractical. A common trap is mistaking this for multiple inheritance, but the key distinction is that composition builds functionality through contained objects rather than inherited methods. Memory tip: think "has-a" for composition versus "is-a" for inheritance—your car has an engine, it is not an engine.
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 developer is designing a system where a `Car` class needs to reuse functionality from `Engine` and `Transmission` without creating a deep hierarchy. Which OOP principle should be applied?
Aggregation, where Car is part of Engine.
Why wrong: Aggregation is a weaker form of composition; the direction is wrong.
Singleton pattern for Engine.
Why wrong: Irrelevant to reusing functionality.
Multiple inheritance to inherit from both.
Why wrong: Inheritance would create a rigid hierarchy; composition is more flexible.
Composition over inheritance.
Car has an Engine and a Transmission, favoring composition.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Composition over inheritance.
Option D, 'Composition over inheritance,' is correct because it advocates building the Car class by composing it with Engine and Transmission objects (has-a relationships) rather than inheriting from them. This avoids a deep class hierarchy and provides flexibility to change or swap components at runtime, which is a key design principle in Python and OOP.
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.
Aggregation, where Car is part of Engine.
Why it's wrong here
Aggregation is a weaker form of composition; the direction is wrong.
Singleton pattern for Engine.
Why it's wrong here
Irrelevant to reusing functionality.
Multiple inheritance to inherit from both.
Why it's wrong here
Inheritance would create a rigid hierarchy; composition is more flexible.
Composition over inheritance.
Why this is correct
Car has an Engine and a Transmission, favoring composition.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Python Institute often tests the distinction between 'is-a' (inheritance) and 'has-a' (composition) relationships, and the trap here is that candidates mistakenly choose multiple inheritance (Option C) because they think reusing functionality requires inheritance, ignoring the complexity and the explicit instruction to avoid a deep hierarchy.
Detailed technical explanation
Composition over inheritance is a principle where a class contains instances of other classes as attributes, enabling code reuse without tight coupling. In Python, this is implemented by assigning Engine and Transmission objects to self.engine and self.transmission in Car.__init__, allowing delegation of methods like start() or shift(). This pattern is favored in real-world systems (e.g., a Car that can swap a gas engine for an electric one) because it adheres to the Single Responsibility Principle and makes testing easier via dependency injection.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
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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: Composition over inheritance. — Option D, 'Composition over inheritance,' is correct because it advocates building the Car class by composing it with Engine and Transmission objects (has-a relationships) rather than inheriting from them. This avoids a deep class hierarchy and provides flexibility to change or swap components at runtime, which is a key design principle in Python and OOP.
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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