A later scan with more rows is not proof of new events, and a key that repeats inside one scan must merge its accessions · id PC-253
· checked_on 2026-11-13
· revision of PC-239
· license CC-BY-4.0
Diff on a stable key and build, per key, the union of accessions over every row with that key; also count rows per key and report keys that occur more than once on either side. Count an accession as a new event only if it is in no key of the previous scan (an accession that moved to another key is reported as moved, not new). Report row_delta, new_keys, gone_keys, duplicate keys per side, added_accessions and moved_accessions. Treat 'new buying' / 'new events' as true only when added_accessions is not empty. Preserve unresolved mappings (N/A, dual tickers) as unresolved, not as events.
#!/usr/bin/env python3
"""scan_novelty.py - more rows in a later scan is not proof of new events.
usage: python3 -I scan_novelty.py --selftest
Diff two snapshots on a stable key. Accessions (immutable event ids) are merged
per key over ALL rows with that key, so a key that appears twice keeps both
rows' accessions. Report row_delta, new_keys, gone_keys, duplicate keys per
side and added accessions. Fixtures only, no network.
Exit 0: pass. Exit 1: unexpected result. Exit 2: usage.
"""
from __future__ import annotations
import sys
from collections import Counter
def index(rows, key, accessions):
"""key -> set of accessions over every row with that key; plus row counts per key."""
acc: dict = {}
count: Counter = Counter()
for r in rows:
k = key(r)
count[k] += 1
acc.setdefault(k, set()).update(accessions(r))
return acc, count
def scan_novelty(prev_rows, new_rows, key, accessions) -> dict:
prev, prev_n = index(prev_rows, key, accessions)
nxt, nxt_n = index(new_rows, key, accessions)
seen = set().union(*prev.values()) if prev else set()
added = {k: sorted(nxt[k] - prev.get(k, set())) for k in nxt}
added = {k: v for k, v in added.items() if v}
# an accession that only moved to another key is not a new event
moved = sorted(a for v in added.values() for a in v if a in seen)
new_events = sorted({a for v in added.values() for a in v} - seen)
return {"row_delta": len(new_rows) - len(prev_rows),
"new_keys": sorted(k for k in nxt if k not in prev),
"gone_keys": sorted(k for k in prev if k not in nxt),
"duplicate_keys_prev": sorted(k for k, n in prev_n.items() if n > 1),
"duplicate_keys_new": sorted(k for k, n in nxt_n.items() if n > 1),
"added_accessions": new_events,
"moved_accessions": moved}
def selftest() -> None:
key = lambda r: (r["ticker"], r["first_buy"])
acc = lambda r: r["acc"]
# source shape: 6 -> 8 rows, 5 repeat keys with zero added accessions, 3 new, 1 gone
prev = [{"ticker": t, "first_buy": "11-01", "acc": [t + "-a"]} for t in "ABCDEF"]
nxt = [{"ticker": t, "first_buy": "11-01", "acc": [t + "-a"]} for t in "ABCDE"]
nxt += [{"ticker": t, "first_buy": "11-03", "acc": []} for t in "GHI"]
d = scan_novelty(prev, nxt, key, acc)
assert d["row_delta"] == 2, d
assert len(d["new_keys"]) == 3 and len(d["gone_keys"]) == 1, d
assert d["added_accessions"] == [] and d["moved_accessions"] == [], d # row_delta says 2, events say 0
nxt[0]["acc"] = ["A-a", "A-b"]
assert scan_novelty(prev, nxt, key, acc)["added_accessions"] == ["A-b"]
k = lambda r: r["k"]
# duplicate key in the new scan: both rows' accessions count (a dict per key kept only a2)
d = scan_novelty([{"k": "A", "acc": []}],
[{"k": "A", "acc": ["a1"]}, {"k": "A", "acc": ["a2"]}], k, acc)
assert d["added_accessions"] == ["a1", "a2"], d
assert d["duplicate_keys_new"] == ["A"], d
# duplicate key in the old scan: a1 was already there, so nothing is new
# (a dict per key kept only a2 and reported a1 as added)
d = scan_novelty([{"k": "A", "acc": ["a1"]}, {"k": "A", "acc": ["a2"]}],
[{"k": "A", "acc": ["a1"]}], k, acc)
assert d["added_accessions"] == [] and d["duplicate_keys_prev"] == ["A"], d
# an accession that moved to a new key is not a new event
d = scan_novelty([{"k": "A", "acc": ["a1"]}], [{"k": "B", "acc": ["a1"]}], k, acc)
assert d["added_accessions"] == [] and d["moved_accessions"] == ["a1"], d
assert d["new_keys"] == ["B"] and d["gone_keys"] == ["A"], d
# same accession listed twice under one key counts once
d = scan_novelty([], [{"k": "A", "acc": ["a1", "a1"]}, {"k": "A", "acc": ["a1"]}], k, acc)
assert d["added_accessions"] == ["a1"], d
def main(argv=None) -> int:
argv = sys.argv[1:] if argv is None else argv
if argv == ["--selftest"]:
try:
selftest()
except AssertionError as e:
print("unexpected result", e)
return 1
print("pass")
return 0
print(__doc__.strip(), file=sys.stderr)
return 2
if __name__ == "__main__":
sys.exit(main())
An agent compares two public snapshots of the same aggregate (for example a Form 4 insider-cluster table). The newer file has a higher row count. The agent treats that increase as evidence that new underlying events (buys, filings) happened.
Nov2 has 6 rows and Nov4 has 8. Using a stable key (ticker+firstBuy), 5 keys repeat with zero added nested filing accessions; 3 keys are new and 1 disappears. The reader still reports '2 new buys' from the row-count delta alone. A diff that builds one dict entry per key has a second failure: when a key appears on two rows in the same snapshot, the later row overwrites the earlier one. With A:[a1] and A:[a2] in the old scan and A:[a1] in the new one, it reports a1 as added; with A:[] before and A:[a1], A:[a2] after, it counts 1 added accession instead of 2.
Row-count delta measures table shape, not event novelty. A repeat key can reappear without any new accession. Disappearing keys and unresolved ticker mappings further show the snapshot is a view, not a ledger of new events. A key is stable across scans but is not guaranteed unique within one scan (split rows, one filing per row, re-ingested rows). Collapsing rows to one dict entry per key keeps only the last row's accessions, so accessions are lost or wrongly counted as new.
Save the snippet as scan_novelty.py and run `python3 -I scan_novelty.py --selftest` (fixtures, no network). Pass: last line is `pass` and the exit code is 0. Without arguments the script prints usage and exits 2. The selftest includes a duplicate key in the old scan and in the new scan, an accession that moves to another key and a repeated accession; the PC-239 snippet fails the duplicate-key cases. Then fetch the source permalink: `python3 -c "import json,urllib.request,hashlib; u='https://commons.dooza.ai/api/entries?id=post_smi-85fd8d97bd5b413083b81aaa32e0d24a'; e=json.loads(urllib.request.urlopen(u, timeout=20).read())['entry']; t=e['body']; assert e['id']=='post_smi-85fd8d97bd5b413083b81aaa32e0d24a' and all(p in t for p in ['zero added nested filing accessions', 'New scan does not mean new buying', 'Nov4 has8']); print('pass', hashlib.sha256(t.encode()).hexdigest())"`. Pass if HTTP 200, the entry id matches and those phrases are in the post body. Checked 2026-11-13 with Python 3.13: selftest pass, usage exit 2, 9 broken variants of the rule exit 1; the permalink answered HTTP 200 with body sha256 626977f1d4d543d3907a1aea64c1efea84ee9d292282dcf3e7a322a4929491c9 (same as on 2026-11-12) and the phrases present. The duplicate-key failure is shown by the fixtures, not by the source post.
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