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 in a single line of code. Which statement correctly accomplishes this?
a = b, b = a
Why wrong: Invalid syntax. This is not a valid assignment.
a = b; b = a
Why wrong: Incorrect. After a = b, the original a is lost, so b = a just sets b to the same value.
a, b = b, a
Correct. This uses tuple unpacking to swap values.
a = b; a = b
Why wrong: Incorrect. This assigns b to a twice and does not swap.
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 C is correct because Python supports tuple unpacking, allowing the values of variables `a` and `b` to be swapped in a single line: `a, b = b, a`. The right-hand side `b, a` creates a tuple of the current values, which is then unpacked and assigned to the left-hand side variables, effectively swapping them without needing a temporary variable.
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
Invalid syntax. This is not a valid assignment.
a = b; b = a
Why it's wrong here
Incorrect. After a = b, the original a is lost, so b = a just sets b to the same value.
a, b = b, a
Why this is correct
Correct. This uses tuple unpacking to swap values.
Related concept
Read the scenario before looking for a memorised answer.
a = b; a = b
Why it's wrong here
Incorrect. This assigns b to a twice and does not swap.
Common exam traps
The trap here is that candidates often confuse the comma-separated assignment syntax with other languages' swap methods (like using a temporary variable or semicolons), leading them to choose Option B, which appears to work sequentially but actually fails due to the overwrite issue.
Detailed technical explanation
Under the hood, `a, b = b, a` evaluates the right-hand side tuple `(b, a)` first, capturing the original values, then unpacks them into the left-hand side variables. This mechanism relies on Python's evaluation order — the right-hand side is fully evaluated before any assignment occurs — which avoids the need for a temporary variable. In real-world scenarios, this is commonly used in sorting algorithms (e.g., bubble sort) and in-place data transformations where conciseness and readability are valued.
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 C is correct because Python supports tuple unpacking, allowing the values of variables `a` and `b` to be swapped in a single line: `a, b = b, a`. The right-hand side `b, a` creates a tuple of the current values, which is then unpacked and assigned to the left-hand side variables, effectively swapping them without needing a temporary variable.
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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