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Find out what this repository is and what the last person said about the state of it.
ls -R . | head -30 && cat README.md.:
CONTRACT.md
README.md
data
load.py
pytest.ini
src
tests
./data:
orders_2026_04.csv
orders_2026_05.csv
./src:
warehouse
showing 16 of 42 lines
Read the contract before the code. The output shape is fixed and the reject reasons are already named, so this is a mapping problem with a spec, not a design decision.
cat CONTRACT.md# Warehouse format contract
The loader turns a vendor order export (CSV) into the warehouse format, plus a rejects
file. Everything downstream of the warehouse reads this contract and nothing else, so it
is the part of this repository that is not allowed to drift.
## The warehouse format
JSON Lines: one JSON object per accepted row, in the order the rows appear in the source
file, UTF-8, newline terminated.
Each object has exactly these eight fields, in this order:
| field | type | meaning |
| --------------- | ------- | ----------------------------------------------------------- |
| `order_id` | string | Vendor order identifier. Never empty. |showing 16 of 81 lines
Reproduce the failure and read the traceback. KeyError on customer_name, so the header changed.
python3 load.py data/orders_2026_05.csv out/orders.jsonl out/rejects.jsonlTraceback (most recent call last):
File "/workspace/load.py", line 20, in <module>
raise SystemExit(main(sys.argv[1:]))
^^^^^^^^^^^^^^^^^^
File "/workspace/src/warehouse/cli.py", line 32, in main
report = transform_file(source, destination, rejects)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/workspace/src/warehouse/pipeline.py", line 96, in transform_file
record = _record(row)
^^^^^^^^^^^^
File "/workspace/src/warehouse/pipeline.py", line 59, in _record
"customer_name": row["customer_name"],
~~~^^^^^^^^^^^^^^^^^
KeyError: 'customer_name'
15 lines, 645 B
Diff the two headers by eye. Four changes: region_code became market, the name is split in two, discount_cents is new and sometimes empty, and the dates are DD/MM/YYYY where the old file was ISO.
for f in data/orders_2026_04.csv data/orders_2026_05.csv; do
echo "== $f"
head -1 "$f"
sed -n 2,3p "$f"
done
6 lines, 115 B
== data/orders_2026_04.csv
order_id,customer_name,region_code,currency,amount_cents,placed_at
SO-41001,Ada Lovelace,eu-west,EUR,125000,2026-04-02
SO-41002,Grace Hopper,us-east,USD,98250,2026-04-02
== data/orders_2026_05.csv
order_id,customer_first_name,customer_last_name,market,currency,amount_cents,discount_cents,placed_at
SO-52001,Radia,Perlman,eu-west,EUR,142000,2000,04/05/2026
SO-52002,Vint,Cerf,us-east,USD,86400,,05/05/2026
9 lines, 433 B
Read the loader. Every source column name is hardcoded in _record, and the only reject reason implemented is bad_amount, because April never needed the others.
{
"path": "src/warehouse/pipeline.py"
}3 lines, 41 B
"""Turn a vendor order export into the warehouse format.
The output contract lives in CONTRACT.md and is the only thing downstream of here that is
guaranteed. Rows that cannot be converted go to the rejects file with a reason, because a
loader that drops a row is worse than a loader that fails: the row is gone and the totals
are quietly wrong.
"""
from __future__ import annotations
import csv
import json
from dataclasses import dataclass
from pathlib import Path
FIELDS = (showing 16 of 106 lines
Find the rows that will not convert, from the data rather than from imagination. Four of them, one for each reason code in the contract, which is what the rejects file has to carry.
python3 -c '
import csv
from datetime import datetime
with open("data/orders_2026_05.csv", newline="") as handle:
reader = csv.DictReader(handle)
for line, row in enumerate(reader, start=2):
problems = []showing 8 of 28 lines
8 ["amount 'not-yet-priced'"]
10 ['order_id blank']
13 ["discount 'pending'"]
16 ["date '32/05/2026'"]
5 lines, 103 B
Put the layout in a table picked by header, so both exports load and the next reshape is one more entry. Checks run in the contract's order, each raising its reason code, and the header is resolved before either output file is opened so a mystery file cannot truncate the last good load.
"""Turn a vendor order export into the warehouse format.
The output contract lives in CONTRACT.md and is the only thing downstream of here that is
guaranteed. Rows that cannot be converted go to the rejects file with a reason, because a
loader that drops a row is worse than a loader that fails: the row is gone and the totals
are quietly wrong.
The vendor reshapes the export from time to time, so the source layout is data rather than
something spread through the code. A layout says where the warehouse fields come from in
one export shape, the header picks the layout, and a header nobody has mapped is refused
instead of guessed at. Adding the next layout is then one more entry in LAYOUTS, and the
old ones keep loading, which they have to: the warehouse reloads history.
"""
from __future__ import annotations
import csv
import jsonshowing 18 of 230 lines
{
"path": "src/warehouse/pipeline.py"
}3 lines, 41 B
Wrote 7431 bytes (230 lines) to src/warehouse/pipeline.py.April's suite first. Backward compatibility is the half of this that is easy to break silently.
python3 -m pytest -q tests..... [100%]
5 passed in 0.02s
3 lines, 98 B
Load both months. The counts have to add up per file, and April's has to be what it was before.
python3 load.py data/orders_2026_05.csv out/orders.jsonl out/rejects.jsonl
python3 load.py data/orders_2026_04.csv out/april.jsonl out/april-rejects.jsonl
wc -l out/*.jsonl
4 lines, 173 B
read 18, wrote 14, rejected 4
read 14, wrote 13, rejected 1
1 out/april-rejects.jsonl
13 out/april.jsonl
14 out/orders.jsonl
4 out/rejects.jsonl
32 total
8 lines, 166 B
Check the record shape against the contract rather than glancing at the file. Field order, the net arithmetic, and every date landing in May, which is the assertion that catches a day and month swap.
python3 -c '
import json
FIELDS = ["order_id", "customer_name", "region", "currency",
"amount_cents", "discount_cents", "net_cents", "placed_on"]
records = [json.loads(line) for line in open("out/orders.jsonl")]
print("records", len(records))
print("field order held", all(list(r) == FIELDS for r in records))showing 8 of 13 lines
records 14
field order held True
net = amount - discount True
months ['2026-05']
split names ['Radia Perlman', 'Vint Cerf', 'Margaret Hamilton']
6 lines, 145 B
Reconcile against the source. Eighteen rows in, fourteen written, four rejected with a reason each, and the accepted identifiers are exactly the source identifiers minus the rejected ones. That is the check that a dropped row cannot pass.
python3 -c '
import csv, json
with open("data/orders_2026_05.csv", newline="") as handle:
source = list(csv.DictReader(handle))
written = [json.loads(line) for line in open("out/orders.jsonl")]
rejected = [json.loads(line) for line in open("out/rejects.jsonl")]
print("read", len(source), "written", len(written), "rejected", len(rejected))showing 8 of 14 lines
read 18 written 14 rejected 4
every row accounted for True
reasons [(8, 'bad_amount'), (10, 'missing_order_id'), (13, 'bad_discount'), (16, 'bad_date')]
ids match True
5 lines, 168 B
Say what changed upstream, what the mapping is now, and give the reconciliation numbers.
May's export renamed region_code to market, split customer_name into customer_first_name and customer_last_name, added an optional discount_cents, and switched placed_at to DD/MM/YYYY. The loader now resolves a layout from the header, so both April's and May's exports load and an unknown header raises instead of being guessed at, and the warehouse fields are unchanged. Validation covers all four contract reasons rather than only bad_amount: May's 18 rows come out as 14 records and 4 rejects (bad_amount, missing_order_id, bad_discount, bad_date), with read equal to written plus rejected and the accepted identifiers reconciled against the source. April still loads 14 rows to 13 records and 1 reject.
2 lines, 707 B
Run ended by the agent.12 steps9 commands0 schema violations1 failed commands0 destructive attempts
The last few kilobytes of the hidden test run, stdout and stderr together, kept for triage. The agent never saw this.
.......... [100%]
10 passed in 0.07s
3 lines, 99 B
Results that cannot be reproduced are not results. When a number moves, this is how you tell whether the model changed or the environment did.