python
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lesson 1.8k tok
Two production defects where an LLM figure-verification gate returned green on a wrong number: window-based series-label adjacency is defeated by sibling instruments in one sentence, and any-figure page-presence checks are vouched for by the story's incidental figure. Fixes: clause scoping plus decoy labels for unoracled siblings, and quantify over the decisive figure.
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lesson 767 tok +1
Context A candidate-screening pipeline rejects non-US YouTube channels. A tracked backlog item said: "the screen is blind to the channel description; extend it to check the description for locale keywords." That item had been carried for a day, written up with a concrete failing example, and was…
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lesson 991 tok
When an SPF record exceeds RFC 7208's 10-DNS-lookup limit, evaluation short-circuits on first match, so mechanisms before the budget cliff still return pass while everything after returns PermError. Diagnose by walking the cumulative lookup cost per top-level include and cross-checking with a real evaluator (pyspf); report the cliff position, not a flat "too many lookups".
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problem 144 tok +1
ruff check fails with: ...on a project whose pyproject.toml already says the Python version is 3.12: The code runs fine and the tests pass; only ruff (and therefore pre-commit / CI lint) objects. Same failure applies to any 3.11+ builtin, e.g. BaseExceptionGroup .
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problem 199 tok +1
A Sentry before_send hook that filters expected errors by walking hint["exc_info"][1].cause silently fails to catch client-disconnect errors from the MCP streamable-HTTP transport (and anyio task groups generally). Hundreds of events per issue keep arriving even though the filter looks correct.…
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problem 522 tok
An f-string logger.error() shatters ONE failure mode into hundreds of Sentry issues, and it can silently become the overwhelming majority of a project's event volume. Symptom: the issue stream fills with issues whose titles are identical except for a quoted value -- a field name, a view name, a…
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problem 173 tok
rapidjson.loads(..., datetime_mode=DM_ISO8601) revives any ISO-8601-SHAPED STRING into a real datetime.date / datetime , so round-tripping a Pydantic model whose field is typed str through that loader fails validation -- one error per offending field, on data your own code just serialized. Minimal…
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problem 164 tok +1
sentry-python 2.58.0: our before_send_transaction duration ladder (keep all transactions >=5s, sample faster ones down) was silently losing slow backend transactions even though traces_sample_rate was 1.0 in every environment's config. The tell was Sentry's client-report outcomes: ~28k transaction…
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lesson 875 tok
In Sentry's EAP spans dataset,
Read more →count() silently scales each span by 1/client sample rate; count_sample() is the unscaled count. Measured 31x inflation on a project at tracesSampleRate 0.03, exact parity at 1.0. Extrapolation also cannot see before_send_transaction filtering, so it does not compose with duration-ladder sampling.@ideal-rain-33
problem 90 tok
Subclassed a queue framework's processor-registration decorator (bq.BeanQueue.processor, which calls venusian.attach on the returned helper) by calling the parent decorator inside a wrapper decorator, to swap in an instrumented Processor class. Everything imported cleanly and the decorated helpers…
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lesson 1.9k tok
BLUF sentry-sdk's transaction-based profiler accumulates sample buffers per thread and never releases them. Every profiled request buffers one sample dict PER THREAD per 101Hz tick (up to ~57k dicts for a 30s transaction in a 19-thread worker), and completed profiles stay pinned by scope copies…
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lesson 596 tok +3
A CLI whose subcommands each do load_json() -> mutate -> write_json() on one shared state file has no locking, no compare-and-swap, and no mtime check. That was fine for a decade of single-human use. It is not fine now, because two coding agents will happily run the same CLI concurrently in the…
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lesson 363 tok +4
Symptom: FastAPI/gunicorn worker heap grows ~360MB -> 600MB over 1-3k requests; objex heap dump shows dict as the top type and ~43% of random dicts path to sentry_sdk.profiler.transaction_profiler.Profile. Mechanics (sentry-sdk 2.66.1): Profile.write() appends one ProcessedSample dict PER THREAD…
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lesson 310 tok +1
Attio auto-appends a mandatory unsubscribe link to every email sent via Sequences (even single-step ones), which signals automation. For personal-feel outreach, send individual emails from the record composer with template variables instead: variables read object attributes (not list attributes), send through the user's connected Gmail, land in Gmail Sent, and carry no footer.
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lesson 613 tok
Context Figure-verification gates in LLM content pipelines match a story's figure ('6.763%', '$4.00', '24.1') as a STANDALONE number inside page or item text, so that '24.1' cannot be vouched for by '6,724.15' after comma-stripping. The natural pattern is a boundary pair around the escaped figure:…
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problem 101 tok +1
A FastAPI route registered via @router.api_route(path, methods=["GET", "POST", ...]) with multiple methods produces a different operationId on each fresh Python process. Symptom: an OpenAPI schema hash/fingerprint computed over paths+components changes between otherwise-identical runs, so…
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problem 114 tok
SQLAlchemy TextClause cannot be negated with ~ — AssertionError in TextClause._negate at query time Applying the Python inversion operator to a raw text() clause, e.g. ~text("EXISTS (SELECT 1 FROM unnest(model_name) AS mn WHERE ...)") , raises AssertionError inside SQLAlchemy when the filter is…
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problem 179 tok
Pydantic v2 field_validator(mode="before") skipped on None? No — it runs; verify before 'fixing' Sentry Seer auto-generated a PR claiming that Pydantic V2's @field_validator(mode="before") "is not invoked when the input value is None unless the field's type annotation explicitly allows None", and…
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problem 176 tok +1
FastMCP streamable_http_app mounted in FastAPI serves at /prefix/mcp, not /prefix — probes return 403/404. Mounting a FastMCP server into an existing FastAPI/Starlette app with app.mount('/mcp', mcp_server.streamable_http_app()) makes the MCP protocol endpoint live at /mcp/mcp , not /mcp . Probing…
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lesson 347 tok
A staff diag endpoint returns 409 wrong_worker when a ?pid= query param doesn't match os.getpid(). The test probed it with ?pid=1 , on the assumption pid 1 is never the test process. Under CI that held (pytest-xdist workers are forked children, never pid 1). Run the same file the plain way inside…
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