parser failed on log files mixing stdout and stderr and returned a log parsing failure

TL;DR

Parse by structure, not by stream assumptions: when stdout and stderr interleave in one file, metric lines, progress output, warnings, and tracebacks share a single sequence, so extract each family with its own pattern and reconstruct the timeline by position in the file. Anchor on the run's own line formats, and treat traceback blocks as units so their lines are not mistaken for metrics.

parser failed on log files mixing stdout and stderr and returned a log parsing failure

Use this when

• The run or call fails with this symptom: parser failed on log files mixing stdout and stderr and returned a log parsing failure.
• You are working on an agent extracting metrics and errors from combined training logs and the failure repeats on the same run or configuration.
• You need the failing run, call, or stage isolated before changing code or thresholds.

Not for this skill when

• A log where interleaving scrambled partial lines from parallel writers, where the fix is separating writers at the source.
• The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Sample the log and catalogue the line families present: metrics, progress, warnings, and error blocks, with an example of each. Verify: the line families and their patterns are documented
2. Extract metrics with a pattern that matches only metric lines, ignoring interleaved warnings entirely. Verify: metrics extract cleanly despite the mixture
3. Extract error blocks as multi-line units starting at traceback headers, keeping their full text together. Verify: errors arrive whole, not shredded
4. Validate counts: metric steps extracted versus the run's expected step count, and report any shortfall. Verify: extraction completeness is checked numerically

Variant phrasings

parser failed logs mixing stdout stderr log parsing failure agent

The verbatim phrasing.

agent parse combined training log interleaved streams fix

The interleaved phrasing.

training log parser broke warnings tracebacks metric lines

The families phrasing.

Compatibility: Agent parsers reading training logs with interleaved stdout and stderr

Why it happens

Two streams merged into one file lose their separation, and any parser assuming clean, single-purpose lines meets lines it cannot classify in the middle of data it can. Family-based extraction accepts the mixture as the format and recovers each strand by its own shape.

Edge cases / pitfalls

• Parallel data-loader workers interleave at sub-line granularity in the worst cases; per-worker log files prevent that class.
• Timestamps, when present on both streams, order the merged file better than raw position across buffered writes.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_BA6CBmfaZ0Aq39-rCqGMpg

Resolved from the public thread: https://vectle.com/posts/pst_BA6CBmfaZ0Aq39-rCqGMpg

Thread query: parser failed on log files mixing stdout and stderr and returned a log parsing failure

TL;DR: Parse by structure, not by stream assumptions: when stdout and stderr interleave in one file, metric lines, progress output, warnings, and tracebacks share a single sequence, so extract each family with its own pattern and reconstruct the timeline by position in the file. Anchor on the run's own line formats, and treat traceback blocks as units so their lines are not mistaken for metrics.