Quick Answer
The correct answer is [1, 2, 3, 4] because Python list assignment creates a reference, not a copy. When you write b = a, both variables point to the exact same list object in memory, so any in-place modification like append() affects the original list visible through a. This concept is a core part of the Certified Entry-Level Python Programmer PCEP exam, often appearing in questions that test your understanding of mutable objects and variable binding. The common trap is assuming b = a creates a new independent list, when in fact it only binds a new name to the existing object. To avoid this mistake, remember the memory tip: assignment is like giving the same object a nickname, not cloning it.
This PCEP practice question tests your understanding of computer programming and python fundamentals. 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.
Given the code: a = [1, 2, 3]; b = a; b.append(4). What is the value of a?
[1, 2, 3, 4]
Both a and b refer to the same list.
Error
Why wrong: No error.
[1, 2, 3]
Why wrong: b is not a copy; it's a reference.
[1, 2, 3, [4]]
Why wrong: append adds element, not nested list.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
[1, 2, 3, 4]
Option A is correct because in Python, variables hold references to objects, not copies. When `b = a` is executed, both `a` and `b` point to the same list object in memory. The `append()` method modifies the list in-place, so the change is visible through both references. Thus, `a` becomes `[1, 2, 3, 4]`.
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.
[1, 2, 3, 4]
Why this is correct
Both a and b refer to the same list.
Related concept
Read the scenario before looking for a memorised answer.
Error
Why it's wrong here
No error.
[1, 2, 3]
Why it's wrong here
b is not a copy; it's a reference.
[1, 2, 3, [4]]
Why it's wrong here
append adds element, not nested list.
Common exam traps
The trap here is that Cisco tests whether candidates understand that assignment with `=` does not create a new copy for mutable objects; many mistakenly think `b = a` creates a separate list, leading them to choose option C.
Detailed technical explanation
Under the hood, Python lists are dynamic arrays stored on the heap, and assignment `b = a` copies the reference (pointer) to the same list object, not the underlying data. This is a fundamental aspect of Python's object model: mutable objects like lists are shared by reference, whereas immutable objects like tuples or integers may exhibit different behavior. In real-world scenarios, this can lead to unintended side effects when passing lists to functions, so explicit copying via `list.copy()` or `copy.deepcopy()` is often necessary.
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
Computer Programming and Python Fundamentals — This question tests Computer Programming and Python Fundamentals — Read the scenario before looking for a memorised answer..
The correct answer is: [1, 2, 3, 4] — Option A is correct because in Python, variables hold references to objects, not copies. When `b = a` is executed, both `a` and `b` point to the same list object in memory. The `append()` method modifies the list in-place, so the change is visible through both references. Thus, `a` becomes `[1, 2, 3, 4]`.
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 11, 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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