The correct output is 20. This occurs because of attribute shadowing in inheritance, where the `Derived` class defines its own `_x` attribute in `__init__`, which hides the `_x` from the `Base` class. When the inherited `get_x` method runs, `self._x` resolves to the instance’s own attribute—the one set in `Derived`—so the method returns 20, not the base class value. On the Certified Associate Python Programmer PCAP exam, this question tests your understanding of how Python’s attribute lookup works in inheritance: the instance namespace is checked before the class hierarchy. A common trap is assuming the inherited method will use the base class attribute, but `self` always refers to the actual object’s namespace. Remember the memory tip: “self sees the shadow, not the source”—the method uses whatever attribute the instance holds, regardless of where the method was defined.
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
Refer to the exhibit.
```python
class Base:
def __init__(self):
self._x = 10
def get_x(self):
return self._x
class Derived(Base):
def __init__(self):
self._x = 20
obj = Derived()
print(obj.get_x())
```
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
20
Option A is correct because the `Derived` class inherits the `get_x` method from the `Base` class, which returns `self._x`. When `obj.get_x()` is called, `self` refers to the `Derived` instance, and `self._x` accesses the `_x` attribute set in `Derived.__init__` (value 20). The `_x` attribute in `Derived` shadows the one in `Base`, so the output is 20.
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.
✓
20
Why this is correct
Derived.__init__ sets _x to 20, and get_x returns it.
Related concept
Read the scenario before looking for a memorised answer.
✗
AttributeError: 'Derived' object has no attribute 'get_x'
Why it's wrong here
get_x is inherited from Base.
✗
10
Why it's wrong here
Base.__init__ is not called, so _x is not set to 10.
✗
AttributeError: 'Derived' object has no attribute '_x'
Why it's wrong here
Derived has _x set in its __init__.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the distinction between attribute shadowing and method inheritance, specifically that a derived class can override an attribute without calling the base class constructor, leading to unexpected values when inherited methods access that attribute.
Detailed technical explanation
How to think about this question
In Python, single underscore prefix `_x` is a naming convention for 'protected' attributes, but it does not enforce access restrictions; it is still a regular attribute. The `Derived` class overrides `__init__` without calling `super().__init__()`, so the `_x` attribute from `Base` is never set on the instance, and the `Derived` constructor sets its own `_x`. This pattern is common in frameworks where a base class initializes shared state, and derived classes must explicitly call `super().__init__()` to preserve it.
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: 20 — Option A is correct because the `Derived` class inherits the `get_x` method from the `Base` class, which returns `self._x`. When `obj.get_x()` is called, `self` refers to the `Derived` instance, and `self._x` accesses the `_x` attribute set in `Derived.__init__` (value 20). The `_x` attribute in `Derived` shadows the one in `Base`, so the output is 20.
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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