← PCAP·Python Institute

Question 452 of 511

Object-Oriented Programming →hardMultiple ChoiceObjective-mapped

Quick Answer

The correct implementation uses the @property decorator to define a getter and the @radius.setter to create a validation setter that raises a ValueError for negative inputs. This is correct because the setter intercepts every assignment to self.radius, including the initial assignment in __init__, ensuring the non-negative invariant is enforced from object creation onward. On the Certified Associate Python Programmer PCAP exam, this pattern tests your understanding of property decorators as a mechanism for controlled attribute access, often appearing in questions about encapsulation and data validation. A common trap is forgetting that __init__ must assign to self.radius (not self._radius) to trigger the setter, or omitting the underscore-prefixed backing attribute entirely. Remember the mnemonic: "Setter guards the gate, even from the constructor's fate."

PCAP Object-Oriented Programming Practice Question

Q: How is Object-Oriented Programming tested on the PCAP exam?

Object-Oriented Programming — This question tests Object-Oriented Programming — Read the scenario before looking for a memorised answer..

Q: What is the correct answer to this Object-Oriented Programming PCAP question?

The correct answer is: class Circle:\n def __init__(self, radius):\n self.radius = radius\n @property\n def radius(self):\n return self._radius\n @radius.setter\n def radius(self, value):\n if value < 0:\n raise ValueError\n self._radius = value — Option C is correct because it uses the @property decorator to define a getter and @radius.setter to define a setter that validates the radius value before assignment. The __init__ method correctly assigns to self.radius, which triggers the setter, ensuring the initial value is also validated. This pattern enforces the invariant that radius is always non-negative.

Q: Why do candidates get Object-Oriented Programming questions wrong on the PCAP exam?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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 wants to ensure that the 'radius' attribute of a Circle class is always non-negative. Which implementation using @property is correct?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.

Question 1hardmultiple choice

Study the full AAA explanation →

A
class Circle:\n def __init__(self, radius):\n self._radius = radius\n def radius(self):\n return self._radius
Why wrong: radius is a method, not a property; access requires parentheses.
B
class Circle:\n def __init__(self, radius):\n self._radius = radius\n @property\n def radius(self):\n return self._radius\n @radius.setter\n def radius(self, value):\n if value < 0:\n raise ValueError\n self._radius = value
Why wrong: Bypasses setter in init, allowing negative radius at creation.
C
class Circle:\n def __init__(self, radius):\n self.radius = radius\n @property\n def radius(self):\n return self._radius\n @radius.setter\n def radius(self, value):\n if value < 0:\n raise ValueError\n self._radius = value
Uses setter in init, validates always.
D
class Circle:\n def __init__(self, radius):\n self.radius = radius\n @property\n def radius(self):\n return self._radius\n def set_radius(self, value):\n self._radius = value
Why wrong: No setter for property; assignment to self.radius will not call set_radius.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

class Circle:\n def __init__(self, radius):\n self.radius = radius\n @property\n def radius(self):\n return self._radius\n @radius.setter\n def radius(self, value):\n if value < 0:\n raise ValueError\n self._radius = value

Option C is correct because it uses the @property decorator to define a getter and @radius.setter to define a setter that validates the radius value before assignment. The __init__ method correctly assigns to self.radius, which triggers the setter, ensuring the initial value is also validated. This pattern enforces the invariant that radius is always non-negative.

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 Circle:\n def __init__(self, radius):\n self._radius = radius\n def radius(self):\n return self._radius
Why it's wrong here
radius is a method, not a property; access requires parentheses.
✗
class Circle:\n def __init__(self, radius):\n self._radius = radius\n @property\n def radius(self):\n return self._radius\n @radius.setter\n def radius(self, value):\n if value < 0:\n raise ValueError\n self._radius = value
Why it's wrong here
Bypasses setter in init, allowing negative radius at creation.
✓
class Circle:\n def __init__(self, radius):\n self.radius = radius\n @property\n def radius(self):\n return self._radius\n @radius.setter\n def radius(self, value):\n if value < 0:\n raise ValueError\n self._radius = value
Why this is correct
Uses setter in init, validates always.
Clue confirmation
The clue word "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
class Circle:\n def __init__(self, radius):\n self.radius = radius\n @property\n def radius(self):\n return self._radius\n def set_radius(self, value):\n self._radius = value
Why it's wrong here
No setter for property; assignment to self.radius will not call set_radius.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Python Institute often tests the subtlety that __init__ must use the property setter (self.radius = radius) rather than directly assigning to the backing attribute (self._radius = radius) to ensure validation applies to the initial value as well.

Detailed technical explanation

How to think about this question

Under the hood, @property creates a descriptor object that intercepts attribute access. When __init__ assigns to self.radius, Python calls the setter method, which validates the value before storing it in self._radius. This pattern is essential for data encapsulation and maintaining class invariants, especially in APIs where object state must remain consistent across all code paths.

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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.

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.

Related PCAP practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

Modules and Packages practice questions

Practise PCAP questions linked to Modules and Packages.

Strings practice questions

Practise PCAP questions linked to Strings.

Object-Oriented Programming practice questions

Practise PCAP questions linked to Object-Oriented Programming.

Exceptions and File I/O practice questions

Practise PCAP questions linked to Exceptions and File I/O.

PCAP fundamentals practice questions

Practise PCAP questions linked to PCAP fundamentals.

PCAP scenario practice questions

Practise PCAP questions linked to PCAP scenario.

PCAP troubleshooting practice questions

Practise PCAP questions linked to PCAP troubleshooting.

Practice this exam

Start a free PCAP practice session

Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.

10 questions 20 questions 30 questions 50 questions Timed 30

PCAP practice-test guide →Study guide →Browse all practice tests

FAQ

Questions learners often ask

What does this PCAP question test?

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 Circle:\n def __init__(self, radius):\n self.radius = radius\n @property\n def radius(self):\n return self._radius\n @radius.setter\n def radius(self, value):\n if value < 0:\n raise ValueError\n self._radius = value — Option C is correct because it uses the @property decorator to define a getter and @radius.setter to define a setter that validates the radius value before assignment. The __init__ method correctly assigns to self.radius, which triggers the setter, ensuring the initial value is also validated. This pattern enforces the invariant that radius is always non-negative.

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: "always". Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

About these practice questions

Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →

How Courseiva writes practice questions · Editorial policy

Last reviewed: Jun 30, 2026

Question Discussion

Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.

Loading comments…

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.