Page 5 of 8~112 min topic

Random forests

Debug n_estimators=1 disguised as a forest in the readiness random forest

Page 5 reproduces and repairs the characteristic failure of the readiness random forest with OOB-style evidence: n_estimators=1 disguised as a forest, or leaking the test row into every tree.

~14 min this pageDebugging

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Reproduce before you repair

Do not start with a speculative fix for the readiness random forest. 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 random-forests.

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Force the failure

from sklearn.ensemble import RandomForestClassifier
bad=RandomForestClassifier(n_estimators=1, random_state=0)
print({'disguised_as_forest': bad.n_estimators==1, 'fix':'raise n_estimators'})

Expected evidence: disguised_as_forest True warning. If you cannot reproduce on demand, you do not yet control the failure mode for random-forests.

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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 random forest with OOB-style evidence, remember the claim you are restoring: majority-vote class, class probability, and evaluation on unused rows are printed.

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Lab notebook: reproduce on command

Store a one-command reproduction for: n_estimators=1 disguised as a forest, or leaking the test row into every tree. The command should use tabular readiness set with one intentionally noisy 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 random forest, retrying will amplify cost without repairing trust around stabilize predictions when one noisy training row flips.

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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 random-forests, the first fix should usually be detect+prevent at the boundary, because n_estimators=1 disguised as a forest, or leaking the test row into every tree is cheaper to stop early than to explain in production prose.

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Why this stage matters for the readiness random forest

At the debugging stage for random-forests, the job is narrower than finishing a product demo. You are creating one progressive evidence piece about tabular readiness set with one intentionally noisy 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: single decision-tree accuracy on the same split.

For this page specifically, success looks like before/after evidence for the characteristic failure while still centering the user decision to stabilize predictions when one noisy training row flips. If you cannot point to a file, command, or assertion that proves that for the readiness random forest, stay on this page instead of advancing.

Random forest glossary

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Before you start

Why this matters

Describe the smallest fixture that triggers n_estimators=1 disguised as a forest. 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: prediction probability in (0,1)?

All responses are required.