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 system administrator is writing a Python script to monitor server uptime. The script reads a log file line by line, parses timestamps, and stores them in a list. It then loops through the list to detect gaps longer than 5 minutes that indicate a crash. However, the script keeps missing crashes. The current loop is a for loop that iterates over the list using indices. The administrator suspects the loop logic. The loop uses 'for i in range(len(timestamps)-1): if timestamps[i+1] - timestamps[i] > 300: print("Crash detected")'. Timestamps are integers representing seconds since epoch. What is the most likely cause of missed crashes and the best fix?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The timestamps list may not be sorted
Option D is correct because the loop assumes timestamps are in chronological order, but if the list is unsorted, adjacent elements may not represent consecutive events, causing the time difference to be negative or misleading, and thus missing actual gaps. Sorting the list before the loop ensures that timestamps[i+1] - timestamps[i] correctly reflects the time between consecutive log entries.
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 loop should use range(len(timestamps)) instead of -1
Why it's wrong here
Would cause index out of bounds; not the cause of missed crashes.
✗
The difference should be computed as timestamps[i] - timestamps[i+1]
Why it's wrong here
Would give negative differences; still unsorted issue.
✗
The comparison should be > 300, but use > 300.0
Why it's wrong here
Integer vs float comparison is not the issue.
✓
The timestamps list may not be sorted
Why this is correct
Unsorted timestamps lead to inaccurate gap detection. Sorting before loop fixes it.
Clue confirmation
The clue words "best", "most likely" 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 assumption that data structures are in the expected order, and the trap here is that candidates focus on off-by-one errors or type issues while overlooking the fundamental requirement that the list must be sorted for pairwise difference logic to work.
Detailed technical explanation
How to think about this question
Under the hood, Python's list iteration with indices does not enforce any ordering; if the log file contains timestamps out of order (e.g., due to buffered writes or multi-threaded logging), the loop will compare non-consecutive events. A real-world scenario is monitoring syslog from multiple sources where timestamps may arrive interleaved; sorting with timestamps.sort() ensures O(n log n) preprocessing but guarantees correct gap detection.
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 timestamps list may not be sorted — Option D is correct because the loop assumes timestamps are in chronological order, but if the list is unsorted, adjacent elements may not represent consecutive events, causing the time difference to be negative or misleading, and thus missing actual gaps. Sorting the list before the loop ensures that timestamps[i+1] - timestamps[i] correctly reflects the time between consecutive log entries.
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: "best", "most likely". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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