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Python for AI work
Write a small Python program that rejects invalid input.
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Python for AI work
Write a small Python program that rejects invalid input.
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Source-based teaching example · Fictional data · Reviewed 2026-10-03. Microsoft Mark · locally synthesized. On a small screen, use fullscreen for diagram details or read the transcript.
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0:00 · What you will learn
Write a small Python program that rejects invalid input.
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Write a small Python program that rejects invalid input.
0:06 · 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.
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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.
0:19 · One useful term
Input validation. Checking input against the rules before using it.
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Checking input against the rules before using it.
0:27 · 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.
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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.
0:42 · Your turn to think
Should every exception be turned into a successful greeting? Pause and decide before continuing.
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Should every exception be turned into a successful greeting? Pause the video if you need more time.
0:58 · 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.
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No. Keep invalid input visibly different from success. Record the run command and Python version, or label a paper trace as unexecuted.
1:11 · Check 1
Test the limit and the case beyond it.
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Test the limit and the case beyond it.
1:16 · Check 2
Keep errors distinct from normal output.
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Keep errors distinct from normal output.
1:22 · Check 3
Record how you ran the program.
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Record how you ran the program.
1:27 · 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.
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Open the lesson Try the new case Check and revise The full task and its requirements are in the linked lesson.
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