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.
Which TWO of the following are valid ways to define a class attribute that is shared by all instances?
Why wrong: This is a type annotation, not a class attribute assignment (though it may be interpreted as such in some contexts, it is not a standard way).
B
class MyClass: def set_attr(self): MyClass.attr = 0
Why wrong: This defines a method that sets a class attribute, but the attribute is not defined at class creation.
C
class MyClass: pass
MyClass.attr = 0
Assigns a class attribute after definition.
D
class MyClass: attr = 0
Defines a class attribute directly.
E
class MyClass: def __init__(self): self.attr = 0
Why wrong: This creates an instance attribute, not a class attribute.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
class MyClass: pass
MyClass.attr = 0
Option C is correct because assigning an attribute directly to the class after its definition (MyClass.attr = 0) creates a class-level attribute that is shared by all instances. Option D is correct because defining an attribute directly inside the class body (attr = 0) also creates a class-level attribute, accessible to all instances unless shadowed by an instance attribute.
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.
✗
class MyClass: attr: int = 0
Why it's wrong here
This is a type annotation, not a class attribute assignment (though it may be interpreted as such in some contexts, it is not a standard way).
✗
class MyClass: def set_attr(self): MyClass.attr = 0
Why it's wrong here
This defines a method that sets a class attribute, but the attribute is not defined at class creation.
✓
class MyClass: pass
MyClass.attr = 0
Why this is correct
Assigns a class attribute after definition.
Related concept
Read the scenario before looking for a memorised answer.
✓
class MyClass: attr = 0
Why this is correct
Defines a class attribute directly.
Related concept
Read the scenario before looking for a memorised answer.
✗
class MyClass: def __init__(self): self.attr = 0
Why it's wrong here
This creates an instance attribute, not a class attribute.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the distinction between class attributes and instance attributes, and the trap here is that candidates confuse type annotations (which do not create attributes) with actual assignments, or think that assigning inside a method (like __init__) creates a class-level attribute when it actually creates 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 accessible via the class itself or any instance (unless overridden by an instance attribute). When you assign 'attr = 0' in the class body, Python stores it in the class namespace at definition time, making it a true class attribute. The trap with type annotations (Option A) is that they are only metadata; Python 3.6+ does not automatically create the attribute from a bare annotation—you must assign a value to create it. This distinction is critical in real-world scenarios like shared configuration or counters 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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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: class MyClass: pass
MyClass.attr = 0 — Option C is correct because assigning an attribute directly to the class after its definition (MyClass.attr = 0) creates a class-level attribute that is shared by all instances. Option D is correct because defining an attribute directly inside the class body (attr = 0) also creates a class-level attribute, accessible to all instances unless shadowed by an instance attribute.
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.
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