This PCAP practice question tests your understanding of strings. 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 log analysis script needs to extract all IP addresses from a string. The IPs are in dotted-decimal format. Which regex pattern will correctly extract them?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
r'(?:[0-9]{1,3}\.){3}[0-9]{1,3}'
Option C is correct because it uses a non-capturing group `(?:...)` to repeat the pattern `[0-9]{1,3}\.` exactly three times, followed by a final octet `[0-9]{1,3}`. This matches the dotted-decimal structure of an IPv4 address (four octets, each 1–3 digits, separated by dots) without introducing extra spaces or overly permissive digit counts, and it avoids capturing unnecessary groups.
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.
✗
r'[0-9]+\. [0-9]+\.[0-9]+\.[0-9]+'
Why it's wrong here
Has a space after first dot, incorrect.
✗
r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}'
Why it's wrong here
Same as B but without non-capturing group; still matches but less efficient.
✓
r'(?:[0-9]{1,3}\.){3}[0-9]{1,3}'
Why this is correct
Matches three groups of 1-3 digits followed by dot, then one more group. Does not validate range beyond 999, but typical for IP extraction.
Related concept
Read the scenario before looking for a memorised answer.
✗
r'\d+\.\d+\.\d+\.\d+'
Why it's wrong here
Matches any digits, not restricted to 0-255.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the distinction between capturing and non-capturing groups, and the trap here is that candidates see option B (which also works) and assume it is correct, but the exam expects the more efficient non-capturing group syntax (C) as the proper regex for extraction without unnecessary overhead.
Detailed technical explanation
How to think about this question
IPv4 addresses are defined by RFC 791 as four octets (0–255) separated by dots. While regex cannot enforce the 0–255 range without additional logic, using `{1,3}` limits the digit count to a maximum of three, which is the correct structural constraint. The non-capturing group `(?:...)` in option C is a performance optimization: it groups the pattern for repetition without storing the matched substring in a backreference, which is useful in log analysis scripts that process large volumes of data. In real-world scenarios, such as parsing firewall logs or web server access logs, using `\d+` (option D) could inadvertently extract invalid strings like '999.999.999.999', leading to false positives.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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.
Strings — This question tests Strings — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: r'(?:[0-9]{1,3}\.){3}[0-9]{1,3}' — Option C is correct because it uses a non-capturing group `(?:...)` to repeat the pattern `[0-9]{1,3}\.` exactly three times, followed by a final octet `[0-9]{1,3}`. This matches the dotted-decimal structure of an IPv4 address (four octets, each 1–3 digits, separated by dots) without introducing extra spaces or overly permissive digit counts, and it avoids capturing unnecessary groups.
What should I do if I get this PCAP 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.
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Question Discussion
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