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 (reads .docx, legacy .doc, .odt and .rtf, decided from the bytes; tolerates Word-authored files — outlineLvl headings, named highlights, unknown constructs degrade to paragraphs)
• 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.

Reading .doc, .odt and .rtf

read() decides the format from the bytes, never a file name, and returns the same document shape for all four:

The compound-file (MS-CFB) and Word binary (MS-DOC) readers are this package's own code: still no dependencies. A document converted from .docx to .doc and .odt by LibreOffice reads back identical to the .docx; the .rtf differs only in a header-row flag LibreOffice does not write. The PHP and Node engines assert the same result on the same bytes (tests/data/formats/report.read.json).

What it cannot read it refuses with UnsupportedFormatException (a ValueError), whose format names what the bytes are: doc for a Word 6/95 or encrypted file, xls, ppt, msg or cfb for another compound file, xlsx, pptx, ods, odp, or unknown. A damaged file in a supported format raises RuntimeError instead.

Document versions as ops

A version history cannot keep a .docx per edit, and hashing the bytes cannot keep a one-word edit small. last_word.diff(a, b) is the op list that turns document a into document b; store diff(newer, older) and a version is the ops that restore it.

import last_word

ops = last_word.diff(before, after)
# [{"op": "blocks.replace", "path": "/blocks/4/rows/1/cells/1/blocks", "index": 0, "block": {...}}]

last_word.reduce(before, ops)                                 # equals `after`, key order aside
last_word.diff(doc, last_word.read(last_word.to_bytes(doc)))  # [] -- a save without a change records nothing

• Exact. reduce(a, diff(a, b)) equals b. The ops are verified by replaying them; if they do not reproduce b, the diff is one doc.replace.
• Small. Every list is aligned by content -- the blocks, a quote's blocks, a list's items and children, a table's rows, a row's cells, a cell's blocks -- so rewording a paragraph inside a table cell is one blocks.replace at that cell's path, and moving a block is one blocks.move.
• Same file, no ops. Documents that write the same file (equivalent(a, b): merged runs, a header row's bold, a dropped empty paragraph) diff to []. Both documents must be valid, because that check writes them.
• Interchangeable with PHP and Node. The same two documents give the same ops, in the same order, as Agent::diff and Agent.diff, so a history written by any engine replays in the others. Equality is therefore PHP's: 1 and 1.0 differ, and so do True and 1.

Blocks have no ids, so a list op names the list by JSON Pointer and the item by index:

insert clamps its index and creates a missing list; remove, replace and move skip an index out of range; move removes at from, then inserts at to. reduce never modifies its input and skips any op whose path, position or key does not resolve. op_schema() is the JSON Schema for one op, for validating ops on the wire or registering the vocabulary as an LLM tool.

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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