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 class has a class attribute that is a list. A developer modifies this list via one instance, and the change is reflected in all other instances. What is the best practice to avoid this unintended sharing?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Initialize the list in `__init__` rather than as a class attribute.
Option B is correct because class attributes are shared across all instances. By initializing the list inside `__init__`, each instance gets its own independent list object, preventing unintended mutation from affecting other instances. This is the standard Python pattern for instance-specific mutable data.
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.
✗
Use a tuple instead of a list.
Why it's wrong here
A tuple is immutable, so modifications would be impossible; this is a workaround but not a general solution for mutable data.
✓
Initialize the list in `__init__` rather than as a class attribute.
Why this is correct
By creating the list in `__init__`, each instance gets its own independent list.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a class method to modify the list.
Why it's wrong here
A class method would still operate on the shared class attribute.
✗
Use `deepcopy` when accessing the list.
Why it's wrong here
Deepcopy would copy the list each time, which is inefficient and doesn't prevent the initial sharing.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the distinction between class-level and instance-level attributes, and the trap here is that candidates mistakenly think using a tuple (immutable) or a class method solves the sharing problem, when the real issue is the location of the mutable object's definition.
Detailed technical explanation
How to think about this question
In Python, class attributes are stored in the class's `__dict__` and are accessed via the instance's MRO (method resolution order). When you mutate a mutable class attribute (like a list) through an instance, you are modifying the object referenced by the class, not creating a new instance attribute. This is a common pitfall in OOP design, especially when modeling shared state like a database connection pool or a configuration cache, where accidental mutation can lead to hard-to-debug bugs across instances.
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 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
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: Initialize the list in `__init__` rather than as a class attribute. — Option B is correct because class attributes are shared across all instances. By initializing the list inside `__init__`, each instance gets its own independent list object, preventing unintended mutation from affecting other instances. This is the standard Python pattern for instance-specific mutable data.
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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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