Quick Answer
The answer is a, b = b, a, which is the correct approach to swap variables without temporary variable in Python. This works because Python evaluates the right-hand side of the assignment as a tuple (b, a) before unpacking it directly into the left-hand variables, performing the swap in a single atomic operation without needing a third variable. On the Certified Entry-Level Python Programmer PCEP exam, this question tests your understanding of tuple unpacking and assignment semantics, a core concept that distinguishes Python from many other languages. A common trap is trying to use a temporary variable or a more complex arithmetic method, but the exam expects you to recognize the simplicity of Python’s built-in swap. Memory tip: think of it as “right side packs, left side unpacks” — the tuple is created and immediately unpacked, so the values exchange places seamlessly.
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 programmer needs to swap the values of two variables a and b without using a temporary variable. Which approach works in Python?
a = b; b = a
Why wrong: Incorrect: both end up with same value.
a, b = b, a
Correct: Python's tuple unpacking swaps values.
a = a ^ b; b = a ^ b; a = a ^ b
Why wrong: Incorrect: works but not recommended; also fails for non-int.
a = b + a; b = a - b; a = a - b
Why wrong: Incorrect: this only works for numbers and is error-prone.
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 the values of a and b to be swapped in a single atomic operation: a, b = b, a. This works by creating a tuple (b, a) on the right-hand side, then unpacking it into the variables on the left, effectively swapping the values without 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
Incorrect: both end up with same value.
a, b = b, a
Why this is correct
Correct: Python's 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
Incorrect: works but not recommended; also fails for non-int.
a = b + a; b = a - b; a = a - b
Why it's wrong here
Incorrect: this only works for numbers and is error-prone.
Common exam traps
Python Institute often tests the misconception that simple sequential assignment (a = b; b = a) works for swapping, leading candidates to overlook Python's tuple unpacking mechanism.
Detailed technical explanation
Under the hood, Python's a, b = b, a uses the bytecode instruction ROT_TWO (for two variables) or BUILD_TUPLE/UNPACK_SEQUENCE for more variables, which swaps references on the stack efficiently. This technique is not just syntactic sugar; it is thread-safe in CPython due to the Global Interpreter Lock (GIL) making the swap atomic at the bytecode level. In real-world scenarios, this pattern is commonly used in sorting algorithms like quicksort or in-place array manipulations where clarity and performance matter.
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 the values of a and b to be swapped in a single atomic operation: a, b = b, a. This works by creating a tuple (b, a) on the right-hand side, then unpacking it into the variables on the left, effectively swapping the values without 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 30, 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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