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 Python developer is implementing a class that should behave like a sequence and support indexing. Which pair of special methods must be defined to achieve this?
__getitem__ and __contains__
Why wrong: __contains__ is for membership testing, not required for sequence behavior.
__setitem__ and __delitem__
Why wrong: These are for item assignment and deletion, not necessary for read-only indexing.
__iter__ and __next__
Why wrong: These are for iteration, not indexing.
__getitem__ and __len__
These are the minimum to support indexing and length.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
__getitem__ and __len__
To make a class behave like a sequence and support indexing (e.g., obj[0]), Python requires the __getitem__ method to retrieve items by key. Additionally, the __len__ method is needed to define the length of the sequence, which is used by built-in functions like len() and is part of the sequence protocol. Together, these two methods satisfy the minimal requirements for a sequence-like object that supports indexing.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
__getitem__ and __contains__
Why it's wrong here
__contains__ is for membership testing, not required for sequence behavior.
__setitem__ and __delitem__
Why it's wrong here
These are for item assignment and deletion, not necessary for read-only indexing.
__iter__ and __next__
Why it's wrong here
These are for iteration, not indexing.
__getitem__ and __len__
Why this is correct
These are the minimum to support indexing and length.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Python Institute often tests the distinction between the sequence protocol (__getitem__ + __len__) and the iterator protocol (__iter__ + __next__), trapping candidates who think iteration alone enables indexing.
Detailed technical explanation
Under the hood, Python's sequence protocol is formally defined by the need for __getitem__ and __len__; when these are present, Python automatically provides iteration, the 'in' operator, and the reversed() function via the built-in __iter__ and __contains__ fallbacks. A subtle behavior is that if __getitem__ raises IndexError for out-of-bounds indices, Python treats the object as a sequence and can iterate over it without __iter__ being defined. In real-world scenarios, this is used for custom data structures like sparse arrays or database-backed collections where indexing must be efficient.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
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FAQ
Object-Oriented Programming — This question tests Object-Oriented Programming — Read the scenario before looking for a memorised answer..
The correct answer is: __getitem__ and __len__ — To make a class behave like a sequence and support indexing (e.g., obj[0]), Python requires the __getitem__ method to retrieve items by key. Additionally, the __len__ method is needed to define the length of the sequence, which is used by built-in functions like len() and is part of the sequence protocol. Together, these two methods satisfy the minimal requirements for a sequence-like object that supports indexing.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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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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