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

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.

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:

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

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

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

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.