The correct change is to move the dictionary initialization into the __init__ method so each instance creates its own dictionary. This resolves the issue because a mutable class attribute like config_cache is shared across all instances of the class; when you modify the dictionary through one instance, the change is reflected in every other instance since they all reference the same object in memory. By assigning self.config_cache = {} inside __init__, each new instance gets its own independent dictionary, preventing unintended shared state. On the Certified Associate Python Programmer PCAP exam, this question tests your understanding of the difference between mutable class attributes and instance attributes, a classic trap where beginners assume each instance gets its own copy of a mutable default. A reliable memory tip: class attributes are shared like a communal whiteboard, while instance attributes are personal notebooks—always initialize mutable objects like lists or dictionaries inside __init__ to avoid surprises.
PCAP Object-Oriented Programming Practice Question
This PCAP practice question tests your understanding of object-oriented programming. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
An application uses a class to represent a configuration object that reads settings from a file. The class has a class attribute config_cache that holds a dictionary of loaded configurations to avoid repeated file reads. However, the developer notices that when they modify the dictionary for one instance, it affects all instances. They want to ensure that each instance has its own copy of the configuration data upon initialization. Which change should they make?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Move the dictionary initialization into the __init__ method so each instance creates its own dictionary.
Option A is correct because moving the dictionary initialization into the __init__ method ensures that each instance gets its own separate dictionary object. Class attributes are shared across all instances, so modifying the dictionary via one instance changes it for all. By assigning `self.config_cache = {}` inside __init__, each instance creates a new, independent dictionary upon instantiation, solving the shared-state problem.
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.
✓
Move the dictionary initialization into the __init__ method so each instance creates its own dictionary.
Why this is correct
Initializing in __init__ creates a new dictionary per instance, avoiding sharing.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a @staticmethod to return a new dictionary each time.
Why it's wrong here
A static method does not affect instance attributes.
✗
Keep the class attribute but use a deep copy in __init__ before modifying.
Why it's wrong here
This would work but is more complex; moving to __init__ is simpler and more Pythonic.
✗
Define the dictionary inside a class method.
Why it's wrong here
A class method still operates on class-level data.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the distinction between mutable and immutable class attributes, trapping candidates who think a deep copy in __init__ will fix the sharing issue, when in fact the shared reference to the class attribute itself must be replaced with an instance attribute.
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 __class__ attribute. When you modify a mutable class attribute (like a dict) through an instance, you are modifying the same object in memory. The __init__ method runs after __new__ creates the instance, and assigning an instance attribute (self.attr) stores it in the instance's __dict__, shadowing the class attribute. This is a fundamental aspect of Python's attribute lookup order: instance → class → parent classes.
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: Move the dictionary initialization into the __init__ method so each instance creates its own dictionary. — Option A is correct because moving the dictionary initialization into the __init__ method ensures that each instance gets its own separate dictionary object. Class attributes are shared across all instances, so modifying the dictionary via one instance changes it for all. By assigning `self.config_cache = {}` inside __init__, each instance creates a new, independent dictionary upon instantiation, solving the shared-state problem.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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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 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?
hard
A.Use a tuple instead of a list.
✓ B.Initialize the list in `__init__` rather than as a class attribute.
C.Use a class method to modify the list.
D.Use `deepcopy` when accessing the list.
Why B: 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.
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Question Discussion
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