200-901 Software Development and Design Practice Question
In Python, which data type is used to represent an unordered collection of unique elements?
⚠ Common exam trap
A common mix-up: candidates confuse a set with a list or tuple because they think 'collection of items' implies order or mutability, but Cisco specifically tests the requirement for uniqueness and lack of order, which only the set satisfies.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
set
In Python, a set is the correct data type for representing an unordered collection of unique elements. Sets automatically enforce uniqueness by using a hash table internally, so duplicate values are ignored upon insertion. This makes them ideal for operations like membership testing and deduplication, where order is irrelevant.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
set
Why this is correct
A `set` stores an unordered collection of unique elements, automatically discarding duplicates on insertion. This directly satisfies the stem's two constraints: no defined ordering, and uniqueness of members. Hash-based storage gives average O(1) membership testing, unlike lists or tuples, which permit duplicates and preserve insertion order.
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tuple
Why it's wrong here
A tuple is an ordered, immutable sequence that permits duplicates, so it cannot represent uniqueness or lack of order. Tuples suit fixed records where position matters; the required type is the set, which stores unordered unique elements.
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list
Why it's wrong here
A list is ordered and permits duplicate values, so it fails both the unordered and unique requirements. Lists are chosen when sequence and duplicates matter; the question asks for the type that enforces uniqueness without order, which is the set.
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dict
Why it's wrong here
A dict stores key-value mappings with insertion-ordered keys, not an unordered collection of unique elements. Dictionaries are chosen when values must be looked up by key; uniqueness applies to keys only, not to the collection's purpose here.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-901 practice question is part of Courseiva's free Cisco 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 200-901 exam.