last-word

Zero-dependency .docx writer + reader for agentic word-processing documents — a JSON document model with markdown bridges. The Python mirror of PHP particle-academy/last-word and Node @particle-academy/last-word. Sister to holy-sheet (xlsx) and dark-slide (pptx).

The point is the Editor round-trip: a WYSIWYG editor (react-fancy Editor) speaks markdown; Word speaks .docx. LastWord bridges the two through one JSON model — from_markdown → to_bytes to export a real Word file, read → to_markdown to import one — with no converter sandwich (python-docx, mammoth, pandoc) in between.

import last_word

# Markdown in…
doc = last_word.from_markdown("""# Q3 Report

Revenue was **up 12%** — see the [dashboard](https://example.com).

- Wins
  - Enterprise renewals
- Risks
""")

# …Word file out.
data: bytes = last_word.to_bytes(doc)
last_word.write(doc, "report.docx")

# And back: .docx → model → markdown for the editor.
imported = last_word.read(data)
markdown = last_word.to_markdown(imported)

The document model

A Doc is {"title"?, "blocks"}. Blocks are JSON-friendly discriminated unions — exactly what an agent emits:

A Run is an inline span: {"text", "bold"?, "italic"?, "underline"?, "strike"?, "code"?, "link"?, "color"?, "highlight"?} (colors are #RRGGBB).

It is plain dicts, deliberately — not dataclasses. The model arrives as loose JSON from an agent and the Validator is the gate. A dataclass would move the gate into a constructor and reject exactly the near-miss emissions validate_and_repair() exists to fix. For editor and type-checker support, last_word.schema.types carries TypedDict definitions of every shape; nothing at runtime constructs or checks against them.

API

Module-level functions — Python's namespace is a module, so the peers' static Agent class becomes the package itself (last_word.agent is the same surface if you prefer the qualified form):

• validate(doc) → structured errors [{"path", "message"}] (empty = valid)
• validate_and_repair(doc) → {"ok", "schema", "errors"} (coerces strings to runs, clamps heading levels, drops unknown block types with the error retained). Never mutates the document you pass in.
• to_bytes(doc) → bytes (deterministic output)
• write(doc, path) → {"path", "bytes", "blocks"} — synchronous
• read(bytes_or_path) / from_bytes(data) → Doc (tolerates Word-authored files — outlineLvl headings, named highlights, unknown constructs degrade to paragraphs, never throws)
• to_markdown(doc) / from_markdown(md) → the Editor bridge (GFM: headings, **/*/~~, inline code, links, nested lists, tables, fenced code, blockquotes, images, ---, <!-- pagebreak -->)
• describe(doc) → plain-text summary (title, block counts, word count)
• json_schema() → JSON Schema (draft 2020-12) for LLM tool-use
• version() → package version

Invalid input raises last_word.SchemaException, which carries the same structured errors list rather than making you re-validate to find out why.

Markdown is lossy only where GFM has no syntax: underline / color / highlight decorations, paragraph alignment and image pixel sizes are dropped on to_markdown; everything else round-trips, page breaks included.

Images are embedded from data URLs (PNG/JPEG); when widthPx/heightPx are omitted the intrinsic size is sniffed from the bytes (PNG IHDR / JPEG SOF) and capped at 6.5in width keeping aspect.

Moving between runtimes

The three engines are the same library. Only the call shape changes:

write is async in Node only because browsers have no synchronous filesystem. PHP and Python are both synchronous, and that is the whole difference.

Cross-language parity, as a test result

The metadata slots match both mirrors exactly: the title lives in docProps/core.xml (dc:title) and a code block's language in a lastword:code:{lang} content-control tag (quotes use lastword:quote). The same file opens in any of the three engines, and title plus code language round-trip in every direction.

That is asserted, not asserted-to. tests/test_parity_php.py drives the PHP writer as a subprocess and requires byte-identical OOXML parts for every fixture, and tests/test_cross_read.py reads a frozen .docx written by the Node writer and compares the recovered model. Run the suite with:

PHP_BIN=/path/to/php python -m pytest

A missing PHP interpreter is a loud skip locally and a hard failure under CI — a parity suite that quietly stops comparing anything reads exactly like one that compares everything.

Whole-.docx byte equality across engines is not a goal and never will be: PHP writes through ZipArchive with its own timestamps and version-made-by, this port writes a fixed 1980-01-01 DOS date. A reader sees parts, never the compression.

Requirements

Python 3.11+. No runtime dependencies, deliberately and permanently — zipfile and xml.etree.ElementTree are standard library and generic infrastructure. An all-in-one office library would own the document model, and the model is the product.

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