The correct debugging strategy is to place a breakpoint inside the loop and step through each row in debug mode. This approach directly isolates the IndexError by allowing you to inspect the actual list structure of each row as the loop iterates, revealing exactly which row lacks the expected column index. On the CompTIA ITF+ FC0-U61 exam, this tests your understanding of systematic debugging techniques and strategies—specifically, that a debugger provides runtime visibility into data flow, whereas a try-except block would only mask the symptom without identifying the root cause. A common trap is to immediately check the CSV file manually, but that doesn’t reveal how the script interprets the data at runtime. Remember the mnemonic: “Break before you patch”—always use a breakpoint to see the data before adding error handlers.
FC0-U61 Software Development Concepts Practice Question
This FC0-U61 practice question tests your understanding of software development concepts. 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 software developer is using an integrated development environment (IDE) to write a Python script that processes a CSV file containing customer data. The script uses a for loop to iterate over rows and calculates a total purchase amount. When the developer runs the script, it throws an error: "IndexError: list index out of range". The developer suspects the error occurs when the script tries to access a column that doesn't exist in some rows. Which debugging strategy should the developer use first to isolate the issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Place a breakpoint inside the loop and step through each row in debug mode.
Using a debugger to step through the loop allows inspection of each row and identification of which row causes the error. Adding a try-except block masks the problem. Checking the file beforehand might not reveal the exact runtime issue. Rewriting the script changes the approach without addressing the root cause.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Rewrite the script to use a dictionary instead of a list.
Why it's wrong here
This changes data structure but does not fix the index issue; it may introduce new bugs.
✗
Add a try-except block to catch the exception and continue processing.
Why it's wrong here
This hides the bug and may cause incorrect results; it does not help isolate the cause.
✗
Examine the CSV file to ensure all rows have the same number of columns.
Why it's wrong here
This could be useful but is not a debugging technique for the script execution; the error may still occur due to logic issues.
✓
Place a breakpoint inside the loop and step through each row in debug mode.
Why this is correct
Debugging allows step-by-step execution to identify which row and column access causes the IndexError.
Clue confirmation
The clue word "first" in the question point toward this answer.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related FC0-U61 subnetting questions on CIDR, address ranges, and subnet selection.
Software Development Concepts — This question tests Software Development Concepts — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Place a breakpoint inside the loop and step through each row in debug mode. — Using a debugger to step through the loop allows inspection of each row and identification of which row causes the error. Adding a try-except block masks the problem. Checking the file beforehand might not reveal the exact runtime issue. Rewriting the script changes the approach without addressing the root cause.
What should I do if I get this FC0-U61 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related FC0-U61 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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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 is debugging a program that is producing incorrect output. Which of the following are common debugging techniques? (Choose three.)
hard
✓ A.Using a debugger
✓ B.Code review
✓ C.Adding print statements
D.Reinstalling the operating system
E.Changing the program requirements
Why A: Common debugging techniques include adding print statements, using a debugger, and performing code reviews. Changing requirements or reinstalling the OS are not debugging techniques.
Last reviewed: Jun 24, 2026
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This FC0-U61 practice question is part of Courseiva's free CompTIA 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 FC0-U61 exam.
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