- A
class Integer: @property def value(self): return self._value; @value.setter def value(self, val): if not isinstance(val, int): raise TypeError; self._value = val
Why wrong: This is a property, not a standalone descriptor used across multiple classes.
- B
class Integer: def __set_name__(self, owner, name): self.name = name; def __set__(self, obj, val): if not isinstance(val, int): raise TypeError; obj.__dict__[self.name]=val
This correctly implements a descriptor with validation and proper storage.
- C
class Integer: def __get__(self, obj, objtype): return obj.__dict__[self.name]
Why wrong: Missing __set__ and __set_name__; only getter.
- D
class Integer: def __set__(self, obj, val): if not isinstance(val, int): raise TypeError; obj.__dict__[self.name]=val
Why wrong: Missing __set_name__ to set self.name; also does not define __get__.
Quick Answer
The correct answer is the class Integer that defines both __set_name__ and __set__ methods. This is the standard Python descriptor protocol for attribute validation: __set_name__ captures the attribute name when the descriptor is assigned in the class body, and __set__ intercepts every assignment to that attribute, checking with isinstance(val, int) and raising a TypeError if the value is not an integer, then storing the valid value directly in the instance’s __dict__ to bypass the descriptor on subsequent reads. On the PCAP exam, this question tests your understanding of how descriptors control attribute access and validation, a core concept in Python’s data model. A common trap is forgetting __set_name__ or trying to use __init__ instead, which won’t receive the attribute name automatically. Memory tip: think “set_name stores the name, set validates the game”—the descriptor needs both to know which attribute to guard and how to enforce the type constraint.
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 developer wants to create a custom descriptor that validates attribute values upon assignment. Which code snippet correctly implements a descriptor that ensures the assigned value is an integer?
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 Integer: def __set_name__(self, owner, name): self.name = name; def __set__(self, obj, val): if not isinstance(val, int): raise TypeError; obj.__dict__[self.name]=val
Option B correctly implements a descriptor by defining both __set_name__ and __set__ methods. __set_name__ stores the attribute name, and __set__ validates that the assigned value is an integer before storing it in the instance's __dict__, which is the standard pattern for descriptors in Python.
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 Integer: @property def value(self): return self._value; @value.setter def value(self, val): if not isinstance(val, int): raise TypeError; self._value = val
Why it's wrong here
This is a property, not a standalone descriptor used across multiple classes.
- ✓
class Integer: def __set_name__(self, owner, name): self.name = name; def __set__(self, obj, val): if not isinstance(val, int): raise TypeError; obj.__dict__[self.name]=val
Why this is correct
This correctly implements a descriptor with validation and proper storage.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
class Integer: def __get__(self, obj, objtype): return obj.__dict__[self.name]
Why it's wrong here
Missing __set__ and __set_name__; only getter.
- ✗
class Integer: def __set__(self, obj, val): if not isinstance(val, int): raise TypeError; obj.__dict__[self.name]=val
Why it's wrong here
Missing __set_name__ to set self.name; also does not define __get__.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the distinction between a property (which is a descriptor but tied to a single attribute) and a reusable descriptor class; the trap here is that candidates may think any class with __set__ is sufficient, forgetting that __set_name__ is required to avoid a NameError when the descriptor is used on multiple attributes.
Detailed technical explanation
How to think about this question
Descriptors work by defining __get__, __set__, and/or __delete__ methods; when a descriptor is a class attribute, Python automatically calls these methods on attribute access. The __set_name__ method (added in Python 3.6) is called at class creation time to inform the descriptor of the attribute name, which is crucial for storing values in the instance dictionary without hardcoding names. In real-world frameworks like Django or SQLAlchemy, descriptors are used for field validation and type coercion.
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.
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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 Integer: def __set_name__(self, owner, name): self.name = name; def __set__(self, obj, val): if not isinstance(val, int): raise TypeError; obj.__dict__[self.name]=val — Option B correctly implements a descriptor by defining both __set_name__ and __set__ methods. __set_name__ stores the attribute name, and __set__ validates that the assigned value is an integer before storing it in the instance's __dict__, which is the standard pattern for descriptors in Python.
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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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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