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.
Exhibit
class MyClass:
__slots__ = ('name', 'age')
def __init__(self, name, age):
self.name = name
self.age = age
obj = MyClass('John', 30)
obj.city = 'New York'
Refer to the exhibit. What happens when the last line is executed?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An AttributeError is raised.
When a class defines `__slots__`, it restricts attribute assignment to only those names listed in `__slots__`. Attempting to assign an attribute not in that list (like `city`) raises an `AttributeError` because the instance has no `__dict__` to store dynamic attributes. The `__init__` method does not override this restriction; it simply initializes the allowed slots.
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.
✗
The attribute 'city' is added dynamically.
Why it's wrong here
__slots__ prevents dynamic attribute creation.
✗
The __slots__ is ignored because __init__ is defined.
Why it's wrong here
__slots__ takes effect regardless.
✗
A syntax error occurs.
Why it's wrong here
No syntax error.
✓
An AttributeError is raised.
Why this is correct
Only attributes in __slots__ can be assigned.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the misconception that `__init__` can override `__slots__` or that `__slots__` only applies to class-level attributes, leading candidates to incorrectly choose option B or A.
Detailed technical explanation
How to think about this question
Under the hood, `__slots__` creates descriptors for each slot name and removes the instance `__dict__` to save memory and enforce a fixed set of attributes. This is particularly useful in memory-constrained environments like embedded systems or when creating millions of lightweight objects (e.g., in game development or data processing). A subtle behavior: if `__slots__` is defined in a parent class but not in a child, the child class will have a `__dict__` unless it also defines `__slots__`.
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.
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: An AttributeError is raised. — When a class defines `__slots__`, it restricts attribute assignment to only those names listed in `__slots__`. Attempting to assign an attribute not in that list (like `city`) raises an `AttributeError` because the instance has no `__dict__` to store dynamic attributes. The `__init__` method does not override this restriction; it simply initializes the allowed slots.
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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Question Discussion
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