The error occurs because the attribute name is mangled to _MyClass__private_attr. Python implements name mangling for any attribute prefixed with a double underscore, transforming __private_attr into _ClassName__private_attr at runtime to prevent accidental access from subclasses or external code. When you attempt to access __private_attr directly from outside the class, Python looks for the mangled name, not the original, resulting in an AttributeError. On the Certified Associate Python Programmer PCAP exam, this tests your understanding of encapsulation and name mangling mechanics—a common trap is assuming double underscores provide true privacy rather than just name obfuscation. Remember that mangling only occurs for names starting with two underscores and ending with at most one underscore; a single trailing underscore does not trigger it. A useful memory tip: think of the double underscore as a "double lock" that renames the key, so you must use the mangled form _ClassName__attr to unlock it from outside the class.
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.
Traceback (most recent call last):
File "test.py", line 10, in <module>
print(obj.__private_attr)
AttributeError: 'MyClass' object has no attribute '__private_attr'
Given that MyClass defines __private_attr in __init__, why does this error occur?
Given that MyClass defines __private_attr in __init__, why does this error occur?
Refer to the exhibit.
Traceback (most recent call last):
File "test.py", line 10, in <module>
print(obj.__private_attr)
AttributeError: 'MyClass' object has no attribute '__private_attr'
Given that MyClass defines __private_attr in __init__, why does this error occur?
A
The attribute name is mangled to _MyClass__private_attr.
Correct – Python's name mangling renames the attribute inside the class to include the class name to avoid accidental overriding.
B
The attribute was not defined in __init__.
Why wrong: False – the exhibit states it was defined in __init__.
C
Private attributes cannot be accessed outside the class.
Why wrong: Misleading – they can be accessed using the mangled name, but direct access is prevented by name mangling, not by a runtime blocker.
D
The attribute is a class attribute not an instance attribute.
Why wrong: False – it was set on self, so it is an instance attribute.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The attribute name is mangled to _MyClass__private_attr.
Python uses name mangling for double-underscore attributes: __private_attr becomes _MyClass__private_attr when accessed outside the class. The external code tries to access __private_attr directly, which is mangled, causing the attribute error.
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 name is mangled to _MyClass__private_attr.
Why this is correct
Correct – Python's name mangling renames the attribute inside the class to include the class name to avoid accidental overriding.
Related concept
Read the scenario before looking for a memorised answer.
✗
The attribute was not defined in __init__.
Why it's wrong here
False – the exhibit states it was defined in __init__.
✗
Private attributes cannot be accessed outside the class.
Why it's wrong here
Misleading – they can be accessed using the mangled name, but direct access is prevented by name mangling, not by a runtime blocker.
✗
The attribute is a class attribute not an instance attribute.
Why it's wrong here
False – it was set on self, so it is an instance attribute.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 PCAP exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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: The attribute name is mangled to _MyClass__private_attr. — Python uses name mangling for double-underscore attributes: __private_attr becomes _MyClass__private_attr when accessed outside the class. The external code tries to access __private_attr directly, which is mangled, causing the attribute error.
What should I do if I get this PCAP question wrong?
Identify which PCAP exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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