fail-loud

# Fail loud **The expensive bugs are not the ones that crash. They are the ones that return a plausible answer.** A crash costs a turn. A silent wrong answer costs whatever was decided on it. Each pattern below is one I shipped this week. ## 1. Never `except: pass` in a data path ```python try: ids = _starter_ids(day) # needs `requests` except Exception: pass # <- swallowed a NameError: requests not imported ``` The recent-form blend became a **no-op that still printed confident, unchanged numbers**. It looked exactly like working code. I only found it because a probability I expected to move did not. ```python except Exception as e: # noqa: BLE001 print(f"[ttsf] recent-form blend unavailable: {e}") ``` If a failure is genuinely acceptable, say so out loud, once, with the reason. If it is not acceptable, let it raise. `pass` is neither. ## 2. `if x:` is not `if x is not None:` ```python if h3: # 0.0 is a VALID recent ERA era = blend(season, h3) ``` A pitcher with three scoreless starts had his form silently ignored, and I only noticed because two runs of the "same" analysis disagreed. For any numeric that can legitimately be `0` (ERA, edge, count, price, delta), use `is not None`. Same family: `x or default` discards a legitimate `0`, `""`, `[]`, and `False`. ## 3. A lookup that finds nothing must not look like one that found something ```python def game_pk(gid): if gid.startswith("mlb-"): return gid.split("-")[-1] return None # every hash-form id, silently unresolvable ``` Every bet on a game whose id came from the other ingest path became **permanently ungradeable**: never settled, never reported, never fed back into the model. No error anywhere. Either handle the other shape or make the caller state what it did with nothing. ## 4. Resources: write then commit, and do not use what you closed - **`kv_set` without a transaction never persisted.** Every run re-discovered an exhausted API quota with a real request, because the note saying "exhausted" was never committed. Check whether your helper commits; if not, wrap it. - **Building a payload dict after `con.close()`** threw `Cannot operate on a closed database`. Compute values while the resource is open; assemble afterwards. ## 5. Do not hardcode a list where a glob is correct ```python PROP_PAGES = ["book_mlb_player_props.html", ...] # three naming schemes exist ``` The readiness check read **17** rows while **246** sat in files whose names were not in the list, and blocked a good card. Twice, because I fixed the list rather than the approach. When names are produced by another program, **enumerate, then filter**, and add the freshness filter you now need because you are seeing every file. ## 6. A display label is not a key ```python m = models.get(_MODEL_KEY.get(_mkt(c))) # _mkt returns "1ST TEAM TO SCORE" ``` Returned `{}` for every market, so a bias correction ran on nothing and reported success. Keys and labels are different types even when both are strings; the moment there is a human-readable name, the machine name must come from the raw field. ## The habit After writing any `except`, any `if <numeric>`, any `.get()`, any lookup that can miss: > **If this silently did nothing, would I be able to tell?** If not, add the print, or the raise, or the `is not None`. The check costs one line. The bug it hides costs a day and, here, real money. ## Related skills Checked 2026-08-21 against the ~100 skills installed here and the public collections before writing this one, after the user asked whether well-made skills already existed. They did for two of the six I drafted, and those were folded into the existing skills rather than duplicated: - `verification-before-completion` - proving a claim before making it. Covers the ground my draft "read-the-artifact" would have; the two failure modes it was missing (grepping your own output for success, and treating a dry run as the artifact) were added to it instead. - `systematic-debugging` - root cause before fixes. - `karpathy-guidelines` - surfacing assumptions, surgical changes. - `ponytail` - whether the thing needs to exist at all. Which is the check I skipped when I wrote six skills without looking for prior art first. Nothing installed or public covered freshness-of-inputs, config-that-nothing-reads, silent-failure patterns, or shell-escaping corruption when authoring files, which is why those four exist.