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 programmer wants to check whether a string `s` is a palindrome (reads the same forwards and backwards, ignoring case and non-alphanumeric characters). Which code snippet correctly implements this?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
clean = ''.join(c for c in s if c.isalnum()); return clean.lower() == clean.lower()[::-1]
Option B is correct because it first filters out non-alphanumeric characters using `c.isalnum()`, then converts the cleaned string to lowercase before comparing it with its reverse via slicing `[::-1]`. This ensures that case differences and punctuation/spaces are ignored, which is required for a proper palindrome check per the problem statement.
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.
✗
s.lower() == s.lower()[::-1]
Why it's wrong here
Does not ignore non-alphanumeric characters; 'A man, a plan, a canal: Panama' would fail.
✓
clean = ''.join(c for c in s if c.isalnum()); return clean.lower() == clean.lower()[::-1]
Why this is correct
Correctly filters and checks case-insensitively.
Related concept
Read the scenario before looking for a memorised answer.
✗
s == s[::-1]
Why it's wrong here
Case-sensitive and includes all characters.
✗
return s.lower() == ''.join(reversed(s.lower()))
Why it's wrong here
`reversed()` returns an iterator; joining it works but compares entire string, not ignoring non-alphanumeric.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the candidate's understanding that a simple case-insensitive comparison is insufficient; the trap is that many candidates forget to remove non-alphanumeric characters, leading them to pick Option A or D, which only handle case but not punctuation or spaces.
Detailed technical explanation
How to think about this question
The `isalnum()` method returns `True` only for alphanumeric characters (letters and digits), which is the standard approach for palindrome validation in many coding challenges. The slicing `[::-1]` creates a reversed copy of the string in O(n) time and memory, while `reversed()` returns an iterator that must be joined into a string for comparison. In real-world applications like text processing or natural language interfaces, ignoring case and punctuation is critical for accurate palindrome 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 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: clean = ''.join(c for c in s if c.isalnum()); return clean.lower() == clean.lower()[::-1] — Option B is correct because it first filters out non-alphanumeric characters using `c.isalnum()`, then converts the cleaned string to lowercase before comparing it with its reverse via slicing `[::-1]`. This ensures that case differences and punctuation/spaces are ignored, which is required for a proper palindrome check per the problem statement.
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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