Fix two more divide-by-zero bugs found by the formalization audit - #1078
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…only) The stacks-normalization loop in ScaleneJSON.output_profiles divided each recorded stack's timings by stats.cpu_stats.total_cpu_samples with no guard. That denominator can be 0.0 while stats.stacks is non-empty: a memory-only run with --stacks records stack entries (from the CPU sampler's stack collection) while it is *memory* activity -- not CPU activity -- that passes the 'nothing to output' gate at the top of output_profiles. With no CPU sample ever recorded, total_cpu_samples stays at its initial 0.0 and the loop raises ZeroDivisionError. The sibling per-file/per-line CPU normalizations (~556, ~1259, ~1337) already guard this; this site was missed. Same bug class as the leak-velocity divide (#1077). Found by re-running the formalization audit's 'every denominator is a claim to verify' sweep across the output path (formal/README.md 'Bugs the formalization found', now three). Guard the loop on total_cpu_samples (raw stack entries preserved when 0). Regression test drives the full output_profiles path, so it crashes pre-fix and passes after.
Bug #1 (fixed in #1077) was an unguarded leak_velocity / stats.elapsed_time in the JSON renderer. Scalene has three separate output renderers (Scalene-Debugging.md); the CLI renderer scalene_output.py:699 (scalene view --cli) carried the identical unguarded divide, which #1077 did not touch. Same reachability as #1: compute_leaks gates on allocation growth rate, not wall-clock time, so a leak can be reported on a sub-millisecond run where elapsed_time is still 0.0 -> ZeroDivisionError. Found by re-running the denominator audit across the CLI output path (the other output.py divides at ~339/~379/~416/~657 are already guarded). Guard the velocity denominator, mirroring the #1077 json.py fix. Regression test added. Also updates formal/README.md + HANDOFF.md (now four bugs found). The takeaway, now recorded in HANDOFF: a fix in one renderer does not cover its siblings -- audit all three.
emeryberger
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This was referenced Jul 1, 2026
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Two more divide-by-zero defects of the same class as #1077, found by re-running the formalization audit's "every denominator is a claim to verify against the code" sweep (
formal/README.md→ "Bugs the formalization found") across all three of Scalene's output renderers.Bug 1 — per-stack CPU normalization (
scalene_json.py)The
stats.stacksnormalization loop divided bystats.cpu_stats.total_cpu_sampleswith no guard. That denominator can be0.0whilestats.stacksis non-empty:--stacksrecords stack entries (the CPU sampler's stack collection runs), but it is memory activity — not CPU — that passes the "nothing to output" gate at the top ofoutput_profiles.total_cpu_samplesstays0.0⇒ZeroDivisionError.Sibling per-file/per-line normalizations (
~556,~1259,~1337) were already guarded; this one was missed. Fix guards the loop (raw stack entries preserved when the total is 0).tests/test_stacks_zero_cpu_samples.pydrives the fulloutput_profilespath — crashes pre-fix, passes after.Bug 2 — CLI-renderer twin of the leak-velocity divide (
scalene_output.py)Scalene has three separate output renderers (see
Scalene-Debugging.md). #1077 fixed the unguardedleak_velocity / stats.elapsed_timeonly in the JSON renderer; the CLI renderer (scalene view --cli,scalene_output.py:699) carried the identical unguarded divide.Same reachability:
compute_leaksgates on allocation growth rate, not wall-clock time, so a leak can be reported on a sub-ms run whereelapsed_timeis still0.0. Fix mirrors the #1077 guard;tests/test_cli_leak_velocity_zero_elapsed.pyadded.The other CLI-path divides (
~339,~379,~416,~657) were audited and are already guarded.Notes
formal/HANDOFF.md: a fix in one renderer does not cover its siblings — audit all three. The formalization "bugs found" tally is now four.