This PCAP practice question tests your understanding of strings. Compare every option against the stated constraints before choosing — the best answer satisfies all requirements, not just the most obvious one. 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 string like 'report.pdf'. Which string method is most appropriate?
str.find('.')
Why wrong: find() returns the index of the first occurrence, not the substring.
str.split('.')[-1]
Splits by '.' and returns the last element, which is the extension.
str.partition('.')[2]
Why wrong: partition() returns a tuple; [2] gives the part after the separator, but split() is more idiomatic.
str.rstrip('.pdf')
Why wrong: rstrip() removes trailing characters matching any in the argument, not suitable for extraction.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
str.split('.')[-1]
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.
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.
str.find('.')
Why it's wrong here
find() returns the index of the first occurrence, not the substring.
str.split('.')[-1]
Why this is correct
Splits by '.' and returns the last element, which is the extension.
Related concept
Read the scenario before looking for a memorised answer.
str.partition('.')[2]
Why it's wrong here
partition() returns a tuple; [2] gives the part after the separator, but split() is more idiomatic.
str.rstrip('.pdf')
Why it's wrong here
rstrip() removes trailing characters matching any in the argument, not suitable for extraction.
Common exam traps
Python Institute often tests the distinction between `partition()` and `split()` — candidates mistakenly choose `partition()` because it seems simpler, but they overlook that `partition()` only splits on the first occurrence, making it unsuitable for extensions in filenames with multiple dots.
Detailed technical explanation
The `split()` method with a delimiter returns a list of substrings; using `[-1]` indexes the last element, which is the extension. However, this approach fails for filenames with no extension (returns the whole string) or with multiple dots (e.g., 'file.tar.gz' returns 'gz'). For robust extraction, `os.path.splitext()` is preferred because it handles edge cases like hidden files (e.g., '.bashrc' returns ('', '.bashrc')).
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
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FAQ
Strings — This question tests Strings — Read the scenario before looking for a memorised answer..
The correct answer is: str.split('.')[-1] — 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 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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