This PCEP practice question tests your understanding of data types, variables, basic i/o and operators. 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 developer needs to swap the values of two variables a and b without using a temporary variable. Which single line of code correctly performs the swap?
a = b; b = a
Why wrong: This assigns b to a, then a (now b) back to b, so both become b
a, b = b, a
Correct: tuple unpacking swaps values
a = a ^ b; b = a ^ b; a = a ^ b
Why wrong: XOR swap works for integers but is not a single line and can be confusing
a = a + b; b = a - b; a = a - b
Why wrong: This arithmetic method works but is not a single line and only for numbers
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
a, b = b, a
Option B is correct because Python supports tuple unpacking, which allows swapping the values of two variables in a single line without a temporary variable. The expression `a, b = b, a` evaluates the right-hand side tuple `(b, a)` first, then assigns the values to `a` and `b` respectively, effectively swapping them.
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.
a = b; b = a
Why it's wrong here
This assigns b to a, then a (now b) back to b, so both become b
a, b = b, a
Why this is correct
Correct: tuple unpacking swaps values
Related concept
Read the scenario before looking for a memorised answer.
a = a ^ b; b = a ^ b; a = a ^ b
Why it's wrong here
XOR swap works for integers but is not a single line and can be confusing
a = a + b; b = a - b; a = a - b
Why it's wrong here
This arithmetic method works but is not a single line and only for numbers
Common exam traps
Cisco often tests the distinction between a single-line swap using tuple unpacking and multi-line approaches (like XOR or arithmetic) that technically work but do not satisfy the 'single line' requirement, leading candidates to mistakenly choose those multi-line options.
Trap categories for this question
Similar concept trap
XOR swap works for integers but is not a single line and can be confusing
Detailed technical explanation
Under the hood, Python's tuple unpacking creates a temporary tuple on the right-hand side, evaluates it completely, then unpacks the values into the left-hand side variables. This mechanism is safe and efficient, avoiding integer overflow issues that could occur with arithmetic swaps in languages with fixed-width integers (e.g., C's `int` overflow). In real-world scenarios, this pattern is commonly used in sorting algorithms and data structure manipulations where concise, readable code is preferred.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the PCEP exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Data Types, Variables, Basic I/O and Operators — This question tests Data Types, Variables, Basic I/O and Operators — Read the scenario before looking for a memorised answer..
The correct answer is: a, b = b, a — Option B is correct because Python supports tuple unpacking, which allows swapping the values of two variables in a single line without a temporary variable. The expression `a, b = b, a` evaluates the right-hand side tuple `(b, a)` first, then assigns the values to `a` and `b` respectively, effectively swapping them.
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 25, 2026
This PCEP 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 PCEP exam.
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