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Japanese Postal CSV splits long fields across multiple rows with duplicated data
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Japan Post's official postal code CSV file (ken_all.csv) contains formatting choices that break standard CSV parsers, including multi-line field splits, unquoted fields with embedded commas, and human-readable parenthetical notes mixed into data fields.
Any system that validates or auto-completes Japanese addresses using the official data must handle these parsing edge cases or produce incorrect results. The issues are severe enough that a dedicated package (posuto) was created to normalize the data into a usable format.
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Rows with neighborhood names over 38 characters or half-width katakana over 76 characters are split across multiple lines, with all other fields duplicated on each line and line breaks inserted at apparently random positions.
Parenthetical notes intended for human readers are embedded directly in data fields, including catch-all exclusions like 'except the following buildings' and ambiguous terms such as 一円 which usually means 'the area surrounding' but is the actual neighborhood name in one case.
The separate romaji file is updated less frequently than the main file, is often out of sync, and produces low-quality transliterations that mangle already-Latin text into unreadable strings.
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