Page 5 of 8~112 min topic

Decision trees

Debug overfit tree with max_depth unrestricted on tiny data in the readiness decision tree

Page 5 reproduces and repairs the characteristic failure of the readiness decision tree on hours × practice tests: overfit tree with max_depth unrestricted on tiny data, or missing feature names in export.

~14 min this pageDebugging

1Learn the idea

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Reproduce before you repair

Do not start with a speculative fix for the readiness decision tree. Force the failure on purpose, save the before output, then change one cause at a time. Retries are allowed only for transient conditions—not for bad input that will fail forever on decision-trees.

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Force the failure

from sklearn.tree import DecisionTreeClassifier

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unrestricted depth on tiny n overfits — keep max_depth small

clf=DecisionTreeClassifier(max_depth=2) print({'max_depth':clf.max_depth,'reason':'limit overfit on tiny n'})


Expected evidence: **max_depth 2 rationale**. If you cannot reproduce on demand, you do not yet control the failure mode for `decision-trees`.

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Repair with a reviewable diff

After repair, rerun the exact reproduction command. Keep the failing fixture as a regression seed for the observability page. For the readiness decision tree on hours × practice tests, remember the claim you are restoring: held-out accuracy is reported and export_text shows the splits used.

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Lab notebook: reproduce on command

Store a one-command reproduction for: overfit tree with max_depth unrestricted on tiny data, or missing feature names in export. The command should use small hours/practice_tests readiness table with one holdout row or a minimal mutant of it. Paste the failing output into notes/failure-before.txt (or your shell scrollback as copied text). After the fix, paste notes/failure-after.txt and keep both.

Retries belong only on transient faults. If the failure is bad input, a bad allowlist, or a logic bug in the readiness decision tree, retrying will amplify cost without repairing trust around predict readiness with a path a human can read aloud.

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Worked judgment

Classify the failure as prevent, detect, contain, or recover—using this lab’s language, not a generic poster. For decision-trees, the first fix should usually be detect+prevent at the boundary, because overfit tree with max_depth unrestricted on tiny data, or missing feature names in export is cheaper to stop early than to explain in production prose.

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Why this stage matters for the readiness decision tree

At the debugging stage for decision-trees, the job is narrower than finishing a product demo. You are creating one progressive evidence piece about small hours/practice_tests readiness table with one holdout row that later pages inherit without redefining success. Keep that fixture small enough to inspect by hand, keep outputs copy-pasteable as text, and refuse to narrate this baseline as if it were a production SLA: majority-class accuracy on the holdout before fitting the tree.

For this page specifically, success looks like before/after evidence for the characteristic failure while still centering the user decision to predict readiness with a path a human can read aloud. If you cannot point to a file, command, or assertion that proves that for the readiness decision tree, stay on this page instead of advancing.

Decision tree glossary

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Before you start

Why this matters

Describe the smallest fixture that triggers overfit tree with max_depth unrestricted on tiny data. Predict the first visible symptom (exception, wrong label, silent empty success). You will compare that prediction with the reproduction below.

Check your understanding

Page assessment

Answer from memory. Completion is saved from this evidence, not from opening the next page.

1. Can you reproduce the failure with a one-command fixture?
2. Did you avoid retrying non-transient bad input?
3. Is before/after evidence saved as text (not only a screenshot)?
4. Does the repair restore the metric path toward: held-out accuracy plus a tree text dump that mentions both features?

All responses are required.