Parsing the Infamous Japanese Postal CSV

The posuto package reformats Japan Post’s notoriously difficult ken_all.csv, which embeds parenthetical notes and splits rows when neighborhood names exceed 38 characters or katakana pronunciations exceed 76 characters, duplicating other fields. The CSV contains extreme cases such as postal code 452-0961 with 66 rows and codes 602-8368/602-8374 that span eight split lines due to Kyoto’s intersection-based addressing.