The correct answer is that class C is a subclass of A, and the call `D().method()` returns 'B' because Python's method resolution order (MRO) for diamond inheritance follows the C3 linearization algorithm. When class D inherits from both B and C, which themselves inherit from A, Python constructs an MRO of `[D, B, C, A, object]`; since D does not define `method`, the interpreter walks this MRO and finds the implementation in B first, executing `return 'B'`. On the Certified Associate Python Programmer PCAP exam, this tests your understanding of how MRO resolves conflicts in multiple inheritance, often appearing in questions about diamond-shaped hierarchies where a common ancestor is shared. A common trap is assuming that C's method would be found before B's, but MRO respects the left-to-right order of base classes in the class definition. Remember the mnemonic: "Depth-first, left-to-right, then up" — but with C3, it's actually "children before parents, and leftmost parent first."
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 A:
def method(self):
return 'A'
class B(A):
def method(self):
return 'B'
class C(A):
def method(self):
return 'C'
class D(B, C):
pass
Refer to the exhibit. Which THREE statements about the class hierarchy are correct?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Calling D().method() returns 'B'
Option B is correct because when `D().method()` is called, Python's MRO (Method Resolution Order) for class D is `['D', 'B', 'C', 'A', 'object']`. Since class D does not define `method`, Python looks up the MRO and finds `method` first in class B. The `return 'B'` in B's `method` is executed, so the call returns 'B'.
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.
✗
D does not have a method named 'method'
Why it's wrong here
D inherits method from B.
✓
Calling D().method() returns 'B'
Why this is correct
B is first in MRO after D.
Related concept
Read the scenario before looking for a memorised answer.
✗
The super() call in B would call C.method
Why it's wrong here
super() in B would call the next class in MRO, which is C, but only if B calls super(). Here, B does not call super().
✓
The MRO of D is ['D', 'B', 'C', 'A', 'object']
Why this is correct
Correct linearization.
Related concept
Read the scenario before looking for a memorised answer.
✓
Class C is a subclass of A
Why this is correct
C explicitly inherits from A.
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 `super()` always calls the immediate parent class, when in fact it follows the MRO of the runtime instance, which can skip or reorder classes in multiple inheritance scenarios.
Detailed technical explanation
How to think about this question
Python's C3 linearization algorithm determines the MRO to ensure consistent method resolution in multiple inheritance, especially with diamond patterns. The `super()` function uses the MRO of the actual instance's class, not the class where it is lexically written; this cooperative multiple inheritance design allows each class to call the next in line, enabling mixin patterns. In real-world frameworks like Django or Flask, understanding MRO is critical when overriding methods in class-based views or mixins to avoid unexpected behavior.
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: Calling D().method() returns 'B' — Option B is correct because when `D().method()` is called, Python's MRO (Method Resolution Order) for class D is `['D', 'B', 'C', 'A', 'object']`. Since class D does not define `method`, Python looks up the MRO and finds `method` first in class B. The `return 'B'` in B's `method` is executed, so the call returns 'B'.
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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