Python for AI work
Write a small Python program that rejects invalid input.
Reviewed: 2026-10-03
Source-based teaching example · Fictional data
Narration: Microsoft Mark · locally synthesized

00:00:00.000 — What you will learn

Write a small Python program that rejects invalid input.

Visual description:
Write a small Python program that rejects invalid input.

00:00:06.583 — The idea

Start with a clear rule for valid input. Test a valid case and cases that must fail. A program should not hide an error by returning a normal-looking answer.

Visual description:
Start with a clear rule for valid input. Test a valid case and cases that must fail. A program should not hide an error by returning a normal-looking answer.

00:00:19.708 — One useful term

Input validation. Checking input against the rules before using it.

Visual description:
Checking input against the rules before using it.

00:00:27.250 — A worked example

The greeter accepts nonempty text with a 100-character limit. A 101-character input must fail. Put the length check after the blank-input check and test both failures.

Visual description:
The greeter accepts nonempty text with a 100-character limit. A 101-character input must fail. Put the length check after the blank-input check and test both failures.

00:00:42.042 — Your turn to think

Should every exception be turned into a successful greeting? Pause and decide before continuing.

Visual description:
Should every exception be turned into a successful greeting?
Pause the video if you need more time.

00:00:58.917 — Why this answer works

No. Keep invalid input visibly different from success. Record the run command and Python version, or label a paper trace as unexecuted.

Visual description:
No. Keep invalid input visibly different from success. Record the run command and Python version, or label a paper trace as unexecuted.

00:01:11.583 — Check 1

Test the limit and the case beyond it.

Visual description:
Test the limit and the case beyond it.

00:01:16.708 — Check 2

Keep errors distinct from normal output.

Visual description:
Keep errors distinct from normal output.

00:01:22.208 — Check 3

Record how you ran the program.

Visual description:
Record how you ran the program.

00:01:27.083 — Now try a different case

Open the lesson and try its different practice case. Use every check in the full task. Watching alone does not mark the lesson complete.

Visual description:
Open the lesson
Try the new case
Check and revise
The full task and its requirements are in the linked lesson.