python-lookups-choose-then-exclude

Date: 2026-09-23. Status: implemented.

Decision. The Python lookups choose the record first, on the whole table, and apply the PO-box and large-user exclusions to the record chosen. A date that an excluded record covers is not_found; it is never answered by an older life. The shared resolver takes several value columns and resolves them as one tuple from one record, a null counting as a value, so a rurality class and its stored reason can never come from different split parts. attach_by_era and attach_rurality reassemble the cohort by position, not index label, and accept an empty cohort. A row with no date gets missing_date in attach, attach_by_era and attach_rurality, rather than deleted, no_edition or before_first_version.

Reason. Review of 9fa39d4 found four faults, all in Python and none in SQL. Excluding PO boxes before choosing the life let the previous-life fallback answer AB10 1WS in 2025 from a 1996 life although a PO-box life covers that date; the SQL chooses the life first and returns no value. Resolving a class and its reason separately, with nulls ignored in the agreement check, gave HS6 5HT class 6 beside outside_polygons and PA66 6BN not_found although both of its parts exist. Label-based reassembly duplicated rows sharing an index label and failed on an empty cohort. A missing date read as a date before the first edition or version. The last two were already in attach_by_era on main.

Evidence. On the built table: AB10 1WS on 2025-01-01 is not_found, and unique with its own value only when PO boxes are asked for; HS6 5HT in 2005-2006 is split_conflict under the report rule and the A part, class 6, by default, as in SQL; PA66 6BN is outside_polygons under both rules. tests/test_lookup.py pins each fault on a small table and the reviewer's postcodes on the built one. No SQL, schema or built data changed.