Quick Answer
The correct answer is `'abc'.index('d')`, as it raises a `ValueError` when the substring is not found. This happens because Python’s `str.index()` method is designed to throw an exception for missing substrings, while `str.find()` and `str.rfind()` return -1 instead. On the Certified Associate Python Programmer PCAP exam, this distinction tests your understanding of exception handling versus safe return values in string methods—a common trap where candidates confuse the two behaviors. The key difference between Python string index vs find lies in error handling: `index()` prioritizes strict validation by raising an error, making it ideal for scenarios where a missing substring should halt execution, whereas `find()` is better for conditional checks. For a quick memory tip, think of `index` as “I need it or I’ll throw a fit,” while `find` simply “returns -1 and moves on.”
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.
Which of the following expressions raises a ValueError?
'abc'.index('a')
Why wrong: Returns 0, no error.
'abc'.find('d')
Why wrong: Returns -1, no error.
'abc'.rfind('d')
Why wrong: Returns -1, no error.
'abc'.index('d')
Substring not found; raises ValueError.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
'abc'.index('d')
Option D is correct because calling `'abc'.index('d')` raises a `ValueError` when the substring is not found. The `str.index()` method in Python is designed to raise this exception for missing substrings, unlike `str.find()` and `str.rfind()`, which return -1.
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.
'abc'.index('a')
Why it's wrong here
Returns 0, no error.
'abc'.find('d')
Why it's wrong here
Returns -1, no error.
'abc'.rfind('d')
Why it's wrong here
Returns -1, no error.
'abc'.index('d')
Why this is correct
Substring not found; raises ValueError.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Python Institute often tests the subtle difference between `index()` (which raises an exception) and `find()`/`rfind()` (which return -1), trapping candidates who assume all substring search methods behave identically on failure.
Detailed technical explanation
Under the hood, `str.index()` uses a substring search algorithm (similar to a naive or optimized search) and explicitly raises a `ValueError` when the substring is absent, making it suitable for cases where the substring must exist. In contrast, `str.find()` and `str.rfind()` return -1 to indicate failure, which is useful for conditional checks without exception handling. This distinction is critical in real-world parsing tasks, such as extracting data from structured strings where missing keys should be handled gracefully.
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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Strings — study guide chapter
Learn the concepts, then practise the questions
Strings practice questions
Targeted practice on this topic area only
All PCAP questions
511 questions across all exam domains
Certified Associate Python Programmer PCAP study guide
Full concept coverage aligned to exam objectives
PCAP practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise PCAP questions linked to Modules and Packages.
Practise PCAP questions linked to Strings.
Practise PCAP questions linked to Object-Oriented Programming.
Practise PCAP questions linked to Exceptions and File I/O.
Practise PCAP questions linked to PCAP fundamentals.
Practise PCAP questions linked to PCAP scenario.
Practise PCAP questions linked to PCAP troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Strings — This question tests Strings — Read the scenario before looking for a memorised answer..
The correct answer is: 'abc'.index('d') — Option D is correct because calling `'abc'.index('d')` raises a `ValueError` when the substring is not found. The `str.index()` method in Python is designed to raise this exception for missing substrings, unlike `str.find()` and `str.rfind()`, which return -1.
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.
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 →
Keep practising
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.
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.