input() vs sys.stdin Showdown
Why plain input() costs you on big tests.
input() vs sys.stdin Showdown is a free Coding Interview Prep lesson on CoddyKit — lesson 1 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 Hidden Cost of input()
Every input() call does extra work behind the scenes. On a few lines that is fine, but contests can throw thousands of lines at you. ⏱️
Why It Adds Up
The slowdown is the per-call overhead: prompts, flushing, and encoding checks repeat on every single line you read.
Meet sys.stdin
The faster path is reading from sys.stdin, the raw input stream. It skips the friendly extras that input() adds for you.
import sys
data = sys.stdinRead One Line Fast
Use sys.stdin.readline() to grab a single line quickly. It behaves like input() but with far less overhead per call.
import sys
line = sys.stdin.readline()Mind the Newline
readline() keeps the trailing newline character. Call .strip() to remove it before you parse the value.
n = int(sys.stdin.readline().strip())Slurp Everything at Once
For the fastest reads, pull the whole input in one shot with sys.stdin.read(), then process the text yourself.
data = sys.stdin.read()Split the Whole Blob
After read(), call .split() to turn all tokens into one flat list. Whitespace and newlines are handled together.
tokens = sys.stdin.read().split()Rebind input for Speed
A common trick is to point input at readline so your old code stays the same but runs faster.
import sys
input = sys.stdin.readlineWhen input() Is Just Fine
If a problem reads only a handful of lines, plain input() is perfectly fine. Save the fast path for big inputs.
Print Has Overhead Too
The same idea applies to output: many print() calls are slow. We will fix that in a later lesson on batching.
Pick the Right Tool
The rule of thumb: small input, use input(); large input, switch to sys.stdin. Matching the tool to N saves you points.
Quick Check
Quick gut check on reading speed.
Recap: Fast Reading
You met sys.stdin as the fast alternative to input(): readline() per line, or read().split() for everything. Match the tool to the input size. ⚡
Frequently asked questions
Is the “input() vs sys.stdin Showdown” lesson free?
Yes — the full text of “input() vs sys.stdin Showdown” 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 “input() vs sys.stdin Showdown”?
Why plain input() costs you on big tests. 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 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “input() vs sys.stdin Showdown” 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