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 administrator uses a Python script to analyze firewall logs. The script reads a CSV file with columns 'src_ip', 'dst_ip', 'action', 'time'. It needs to build a list of source IPs that have been blocked more than 3 times. The current code:
blocked_count = {}
blocked_ips = []
for row in logs:
if row['action'] == 'block':
if row['src_ip'] in blocked_count:
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a counter from collections module
Option D is correct because using `collections.Counter` replaces the manual dictionary increment logic with a single optimized C-level operation, reducing Python bytecode execution overhead. The Counter's `most_common()` method or direct iteration over items still requires a second loop, but the first loop's increment is significantly faster due to internal C implementation, which is the primary bottleneck in large log processing.
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.
✗
Use a list comprehension for the second loop
Why it's wrong here
May be slightly faster but still relies on manual counting.
✗
Pre-allocate the blocked_ips list
Why it's wrong here
Cannot pre-allocate size for unknown number of IPs.
✗
Use a set for blocked_ips to avoid duplicates
Why it's wrong here
IPs are already unique from dict keys; set does not improve counting performance.
✓
Use a counter from collections module
Why this is correct
Counter is optimized for frequency counting.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates focus on the second loop's syntax (list comprehension) or data structure (set) instead of recognizing that the first loop's manual counting logic is the real performance bottleneck, which `Counter` optimizes via C-level internals.
Detailed technical explanation
How to think about this question
Under the hood, `collections.Counter` is a subclass of `dict` that uses a C-optimized `__missing__` hook to handle missing keys, and its `update()` method processes iterables in a single C loop. For large CSV logs (e.g., millions of rows), this avoids Python-level attribute lookups and method calls for each row, which can yield 2-5x speed improvements. A real-world scenario is analyzing firewall logs from a busy enterprise network where even microsecond savings per row translate to minutes of total runtime.
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: Use a counter from collections module — Option D is correct because using `collections.Counter` replaces the manual dictionary increment logic with a single optimized C-level operation, reducing Python bytecode execution overhead. The Counter's `most_common()` method or direct iteration over items still requires a second loop, but the first loop's increment is significantly faster due to internal C implementation, which is the primary bottleneck in large log processing.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.