Read N Lines and Edge Cases
Loop over lines and handle trailing whitespace.
Read N Lines and Edge Cases is a free Coding Interview Prep lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Coding Interview Prep learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
The N-Then-Lines Pattern
A classic input format gives a count N first, then N lines of data. Read the count, then loop exactly N times.
Read the Count First
Pull the first line and turn it into an integer with int(). That number controls how many more lines you read.
n = int(input())Loop Exactly N Times
Use range(n) so you read precisely the lines the problem promises, no more and no less.
for _ in range(n):
line = input()Collect Lines into a List
Gather the lines as you go so you can process them later. A list comprehension does it in one tidy line.
rows = [input() for _ in range(n)]Strip Trailing Whitespace
Hidden spaces or newlines can break comparisons. Call .strip() to clean each line before you use it.
line = input().strip()Watch for Blank Lines
An empty line becomes "" after stripping. Decide whether to skip it or treat it as meaningful data.
Read Until EOF
Some problems give no count. Loop over sys.stdin directly to read every line until the input ends.
for line in sys.stdin:
process(line)Handle the Zero Case
When N is zero, your loop should simply do nothing. Make sure the rest of your code still prints a valid answer.
Avoid Off-by-One Reads
Reading one line too few or too many is a common trap. Match your loop count to N exactly to stay aligned.
Tokens May Span Lines
If you slurped everything with read().split(), line breaks vanish. Treat the input as a flat stream of tokens instead.
it = iter(sys.stdin.read().split())Pull Tokens One by One
With an iterator you can grab the next token on demand, ignoring how the values were spread across lines.
n = int(next(it))Quick Check
Reading exactly N lines, what is the risk?
Recap: N Lines & Edges
You can now read a count then loop N times, strip whitespace, handle N=0 and EOF, and dodge off-by-one reads. 🧹
Frequently asked questions
Is the “Read N Lines and Edge Cases” lesson free?
Yes — the full text of “Read N Lines and Edge Cases” is free to read here on the web, and the Coding Interview Prep course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Coding Interview Prep course, upgrade to CoddyKit PRO.
What will I learn in “Read N Lines and Edge Cases”?
Loop over lines and handle trailing whitespace. You practise Coding Interview Prep with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Coding Interview Prep?
No prior experience is required. Coding Interview Prep on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Read N Lines and Edge Cases” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Coding Interview Prep lesson?
Yes. Every Coding Interview Prep lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- input() vs sys.stdin Showdown
- Parse Many Numbers on One Line
- Batch Output the Right Way
- Read N Lines and Edge Cases