Quick Answer
The answer is filename.rsplit('.', 1)[-1] because rsplit performs a right-to-left split, isolating the last dot and returning the extension as the final element. This method is essential when filenames contain multiple dots, such as 'archive.tar.gz', where a standard split('.') would break on every dot and fail to correctly extract only the final extension. On the Certified Associate Python Programmer PCAP exam, this question tests your understanding of string methods and indexing, specifically how rsplit with a maxsplit argument prevents common errors from multiple delimiters. A frequent trap is assuming split('.')[-1] works universally, but it returns the wrong segment when dots appear earlier in the name. To remember: think of rsplit as "reverse split" — it starts from the right, so you always grab the last piece. Memory tip: "Right split, right result" — use rsplit when you only want the final extension.
This PCAP practice question tests your understanding of strings. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 developer needs to extract the file extension from a filename like 'document.pdf'. Which expression returns 'pdf'?
filename.split('.')[1]
Why wrong: Works only if there is exactly one dot; fails for multiple dots.
filename.split('.')[0]
Why wrong: Returns the part before the first dot, not the extension.
filename.rsplit('.', 1)[-1]
Splits from right at the last dot, returning the extension correctly.
filename[-3:]
Why wrong: Assumes extension is exactly 3 characters; fails for '.ini' or '.jpeg'.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
filename.rsplit('.', 1)[-1]
Option D (rsplit('.',1)[-1]) correctly splits from right at the last dot. Option C (split('.')[-1]) fails if multiple dots exist. Option A returns prefix. Option B assumes fixed length.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
filename.split('.')[1]
Why it's wrong here
Works only if there is exactly one dot; fails for multiple dots.
filename.split('.')[0]
Why it's wrong here
Returns the part before the first dot, not the extension.
filename.rsplit('.', 1)[-1]
Why this is correct
Splits from right at the last dot, returning the extension correctly.
Related concept
Read the scenario before looking for a memorised answer.
filename[-3:]
Why it's wrong here
Assumes extension is exactly 3 characters; fails for '.ini' or '.jpeg'.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
Identify which PCAP exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Strings — This question tests Strings — Read the scenario before looking for a memorised answer..
The correct answer is: filename.rsplit('.', 1)[-1] — Option D (rsplit('.',1)[-1]) correctly splits from right at the last dot. Option C (split('.')[-1]) fails if multiple dots exist. Option A returns prefix. Option B assumes fixed length.
Identify which PCAP exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A developer needs to extract the file extension from a string like 'report.pdf'. Which string method is most appropriate?
easyWhy B: Option B is correct because `str.split('.')[-1]` splits the string at each dot and returns the last element, which is the file extension. This method works reliably for simple cases like 'report.pdf' and is a common Python idiom for extracting extensions.
Last reviewed: Jun 24, 2026
This PCAP 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 PCAP exam.
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