PCEP Control Flow, Loops, Lists and Logic Practice Question
This PCEP practice question tests your understanding of control flow, loops, lists and logic. 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 network engineer writes a script to validate IP addresses. The script checks each octet and prints 'Valid' if all octets are between 0 and 255, otherwise 'Invalid'. However, the script always prints 'Invalid' for valid IPs. The code uses a for loop with an else clause. Which logical error is likely?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The for loop's else clause executes when the loop completes without break, but the engineer expects else to run when break occurs
Option D is correct because in Python, a `for` loop's `else` clause executes only when the loop completes normally (i.e., without hitting a `break`). The engineer likely intended the `else` to run when an invalid octet is found (triggering a `break`), but instead the `else` runs when all octets are valid and the loop finishes without breaking, causing the script to always print 'Invalid' when the validation logic is inverted.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The list of octets is not properly split
Why it's wrong here
Would cause errors earlier, not always 'Invalid'.
✗
The condition uses 'or' instead of 'and'
Why it's wrong here
Would cause incorrect validation, but not specifically related to for-else.
✗
The else clause is indented incorrectly
Why it's wrong here
Indentation errors would likely cause SyntaxError, not always 'Invalid'.
✓
The for loop's else clause executes when the loop completes without break, but the engineer expects else to run when break occurs
Why this is correct
Common misunderstanding of for-else; else runs on normal completion.
Clue confirmation
The clue word "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the `for...else` behavior by reversing the expected logic, trapping candidates who assume `else` runs only on error or break, rather than on normal loop completion.
Detailed technical explanation
How to think about this question
The `for...else` construct in Python is unique: the `else` block executes after the loop finishes all iterations unless a `break` statement is encountered. This is often used for search patterns (e.g., checking if an item exists in a list). In IP validation, a common pattern is to `break` on an invalid octet and use `else` to confirm all octets are valid. Misunderstanding this behavior leads to the described bug, where the `else` block runs on successful validation instead of failure.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Control Flow, Loops, Lists and Logic — This question tests Control Flow, Loops, Lists and Logic — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The for loop's else clause executes when the loop completes without break, but the engineer expects else to run when break occurs — Option D is correct because in Python, a `for` loop's `else` clause executes only when the loop completes normally (i.e., without hitting a `break`). The engineer likely intended the `else` to run when an invalid octet is found (triggering a `break`), but instead the `else` runs when all octets are valid and the loop finishes without breaking, causing the script to always print 'Invalid' when the validation logic is inverted.
What should I do if I get this PCEP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "always". Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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