carve (Python binding)

Native Python bindings for the Carve markup language. This package is a thin PyO3 binding over the Rust implementation carve-rs, so the parser is not reimplemented in Python: every conversion delegates to the same engine the Rust CLI and WASM builds use. Output is byte-identical to carve-rs for the same input.

This unlocks the Python docs / data ecosystem (MkDocs, Sphinx, Pelican, Jupyter/nbconvert) for Carve.

Install

Wheels are abi3 (abi3-py38), so a single wheel covers CPython 3.8+.

From a built wheel:

pip install carve-lang

From source (needs a Rust toolchain, 1.75+):

pip install maturin
maturin develop --release      # build + install into the active venv
# or
maturin build --release        # produce a wheel under target/wheels/

Usage

import carve

print(carve.__version__)

# Core conversion (no extensions)
html = carve.to_html("# Hello *world*")
# -> '<section id="Hello-world">\n  <h1>Hello <strong>world</strong></h1>\n</section>'

# Inline emphasis: /italic/ and *bold*
carve.to_html("/italic/ and *bold*")

# Enable opt-in extensions by name
html = carve.to_html(source, extensions=["math_block", "list_table"])

# Configure enabled extensions (the mapping is keyword-only)
html = carve.to_html(
    source,
    extensions=["heading-permalinks", "tabs"],
    extension_options={
        "heading-permalinks": {"aria_label": "Back to text", "lowercase_ids": True},
        "tabs": {"mode": "aria"},
    },
)

# Dedicated explicit-list variant
html = carve.to_html_with_extensions(source, ["autolink"])

# Map `:name:` symbols to their values
carve.to_html("Ship it :rocket:", symbols={"rocket": "🚀"})
# -> '<p>Ship it 🚀</p>'

# Engine-level options are keyword-only. Omitting one preserves its engine default.
carve.to_html("# Mixed Case", lowercase_heading_ids=True)
carve.to_html("Hello @ada", mention_url="https://example.com/{}")

# Other renderers. They take the same engine options and `extension_options`.
carve.to_markdown(source)
carve.to_plain_text(source)
carve.to_ansi(source, lowercase_heading_ids=True)
carve.to_carve(source)

# `strict` turns a writer refusal into a `ValueError` instead of returning the
# source unchanged.
carve.to_carve(source, strict=True)

# Migration returns canonical Carve plus a machine-readable loss report.
carve.from_html('<p>Hello <strong>world</strong></p>')
carve.from_markdown('*em* and **strong**')

# Discover supported extension names
carve.extensions()

Passing an unknown extension name raises ValueError. extension_options only accepts enabled extension names and their documented option keys; unknown names, unknown keys, invalid enum values and options for an extension that takes none are rejected instead of silently using defaults.

The names come from the engine itself, so carve.extensions() is the list this build actually accepts rather than a list documented here that could fall behind it. They are kebab-case (math-block, table-of-contents); the snake_case spellings this binding has always taken (math_block) reach the same extensions, so nothing written against the older names has to change.

Linting

carve.lint reports constructs that parse and render, but not the way the author meant. The defect class it catches is the silent one: the document parses, the renderer emits something, and what the author wrote never reaches the page.

import carve

for warning in carve.lint("{#orphan .cls}\n\n"):
    print(warning["line"], warning["rule"], warning["message"])

1 unattached-block-attribute This block attribute reaches no block: ...

That one is the clearest case - {#id .cls} above a blank line attaches to nothing, so the id and the class vanish and nothing anywhere says so.

Each warning is a dict:

start and end slice the offending text directly:

source = "{#orphan .cls}\n\n"
warning = carve.lint(source)[0]
assert source[warning["start"]:warning["end"]] == "{#orphan .cls}"

They are CODEPOINT offsets, not the byte offsets the Rust API reports. That conversion is deliberate and tested: a Rust caller slices &str with bytes, but Python slices by codepoint, so passing them through unconverted mis-slices every document carrying one non-ASCII character before a warning. The unit follows the host language - carve-js converts the same positions to UTF-16 for the same reason.

extensions is the only option accepted, because it is the only one the engine's linter reads:

carve.lint(source, extensions=["details"])

The parsed AST

carve.parse() returns the document as Python data - the PART 12 exchange shape, the same tree every Carve engine publishes, so a consumer written against one implementation reads another's output.

ast = carve.parse("# Title\n\nBody[^a].\n\n[^a]: note\n")

ast["type"]                        # "document"
[c["type"] for c in ast["children"]]   # ["heading", "paragraph", "footnote"]
ast["children"][0]["pos"]          # {"startLine": 1, "startColumn": 1, ...}

carve.parse_json(source)  # the same tree, as JSON bytes

The root carries exactly type, children and srcByteLength; frontmatter and footnote definitions are block nodes inside children, not root fields. Every node except the root carries pos when the engine could place it - 1-based lines and columns, 0-based offsets, ends exclusive, counted in Unicode codepoints, not bytes. A node the engine could not place, such as reassembled table-cell text, carries no pos at all rather than an invented one.

The serialization is the engine's own, so this binding publishes byte-identical output to the carve --json CLI and to every other binding over carve-rs.

Every rendering entry point (to_html, to_html_with_extensions, to_markdown, to_plain_text, to_ansi, parse and parse_json) also accepts keyword-only lowercase_heading_ids, positions, sections, source_lines, mention_url, tag_url, and profile_base_host. Boolean options accept True or False; URL/host options accept strings. When omitted, each option retains the engine's own default.

The keyword set is the same on every target so a host does not have to remember which target takes which. Most of these options describe HTML markup, so on to_markdown / to_plain_text / to_ansi they have nothing to change; lowercase_heading_ids does change those three, because all four renderers resolve </#id> crossrefs through the same heading index.

Includes

carve.render_with_includes() renders a file-backed document with its {{ path }} includes expanded, contained to a root you name:

import carve

result = carve.render_with_includes(
    open("book/main.crv").read(),
    "/srv/book",                  # containment root, absolute
    source_path="main.crv",       # or absolute; relative is read from the root
)
result["output"]        # the rendered HTML
result["dependencies"]  # every target touched, for a watcher
result["warnings"]      # what degraded, and where

The string entry points (to_html and friends) take no root and expand nothing - a directive stays literal there, so a caller who never opted in never touches the filesystem.

The root must be absolute. A relative value names no root: every canonicalizer resolves one against the process working directory, which is arbitrary with respect to the document, so include_root=".." would silently root containment at the parent of wherever the build ran. It raises ValueError instead. Absolutize it yourself if you have a relative directory in hand, where the decision is visible.

Nothing resolves outside the root. A ../ climb, a symlink pointing out, and an absolute path are all refused after canonicalization, so a path that leaves the root by any spelling is denied rather than read.

Each dependency is a dict:

Refused targets are listed too. A host that watched only what it read would never learn that a missing target now exists, so the preview would stay stale at the moment the author fixes it.

Each warning carries rule, message and file (the document it arose in, root-relative, or None for a root document given no source_path). The engine reports a containment denial and a missing file alike as include-unresolved, so a warning shown to a reader cannot be used to probe the filesystem. suppressed_warnings counts the ones past max_warnings, so a capped report is never read as a clean one.

target selects the renderer: "html" (default), "markdown", "plain" or "ansi". extensions, profile, symbols, renderers and the engine options work as they do on to_html, and an extension applies to an included child exactly as it does to the parent. The budgets - max_depth, max_bytes, max_resolver_calls, max_warnings and the per-file max_file_bytes - pass through to the engine; omit one to keep its default.

Symbols

A :name: symbol renders its literal :name: source unless the name is in the symbols map passed as the symbols= keyword (supported by to_html and to_html_with_extensions):

carve.to_html("Ship it :rocket: :shrug:", symbols={"rocket": "🚀"})
# -> '<p>Ship it 🚀 :shrug:</p>'   (an unmapped name stays literal)

The leading word-boundary guard is unaffected by an active map: a:b:c, 10:30: and me@example.com never become symbols.

Security: symbol values are TRUSTED RAW output. A mapped value is inserted into the output unescaped - the same trust class as a renderers callable. symbols={"b": "<b>x</b>"} emits a real <b> element, not escaped text. This is deliberate (processor configuration is trusted). Never build a symbols map out of untrusted / user-supplied input.

Untrusted input

Carve's normative hardening is always on and needs no argument: dangerous URL schemes are blanked, event-handler attributes like onclick are dropped, and the bidi override/isolate characters behind Trojan Source are removed from rendered text.

Raw passthrough is the deliberate exception. A ```=html block or a `…`{=html} span renders verbatim by design, so it is the one thing input you did not author has to switch off:

html = carve.to_html(user_input, safe=True, profile="comment")

safe=True escapes those raw blocks and spans instead of emitting them. It is HTML-only, because HTML is the only target that can emit live markup: to_markdown escapes raw HTML, to_plain_text drops it, to_ansi keeps it as terminal text.

profile restricts which constructs are allowed at all and caps input length - "full", "article", "comment", "minimal", or None. It applies to every target, including to_markdown / to_plain_text / to_ansi.

An unknown profile name raises ValueError, and so does a rejection - input past the profile's max length, or a denied construct when the action is error:

carve.to_html("x" * 20_000, profile="minimal")
# ValueError: Profile violations: 'document' is not allowed: max_length_exceeded (...)

It raises rather than returning something that looks like output: the engine's infallible entry point answers a rejection with an empty string, which a caller cannot tell from a document that legitimately rendered to nothing.

An engine panic raises carve.EnginePanicError, an Exception subclass. A panic means the engine reached a state it believed impossible, so the document is not renderable, but the interpreter is unaffected and a host can answer the request instead of losing the worker:

try:
    html = carve.to_html(user_input, safe=True, profile="comment")
except carve.EnginePanicError as panic:
    logger.error("carve engine panic: %s", panic)
    html = "<p>This document could not be rendered.</p>"

Before it existed, PyO3 raised its own PanicException, which derives from BaseException, so the except Exception a host actually writes walked past it (#94). The message carries the panic text and its location in the engine source, and the usual thread '<unnamed>' panicked at ... report still reaches stderr, so RUST_BACKTRACE=1 works as before. Treat any input that raises it as an engine defect worth reporting, not as a rejection: a rejection is a ValueError.

Full recipe, defaults and threat model: Security.

Stored documents and spec versions

carve fmt --stamp (in any Carve engine) records the spec version a document was last processed under. This binding reads that marker back, so a repository of stored .crv files can be checked for documents predating a breaking spec change:

carve.read_stamp(source)
# {'version': '0.1', 'generated_by': 'carve-php 0.1.0'}

carve.needs_review(source)   # True when the document predates this engine

An unstamped document answers True: its provenance is unknown, and assuming it is current is the unsafe direction. Both marker forms are read, and a marker written by any engine reads the same - the format is the contract, not any one API.

What a version difference means is the versioning contract: only [behavior] changelog entries between the stamped version and yours can require a document change.

Supported extensions

The string passed in extensions=[...] maps to a carve-rs extension:

Formatting source

carve.to_carve(source) writes the engine's canonical spelling of a document. The writer can refuse a tree it cannot spell back, and by default that refusal comes back as the source as authored - the same value a document that was already canonical returns, so a caller cannot tell the two apart. Pass strict=True to get the refusal as a ValueError:

try:
    formatted = carve.to_carve(source, strict=True)
except ValueError as refusal:
    print(f"left as authored: {refusal}")

A tool that writes the result back to the file wants strict=True: without it, the one document that could not be formatted is reported as formatted.

Write source from AST JSON

carve.render_ast_json(json_text) validates an interchange tree through the native engine and writes Carve source. Invalid JSON, unknown node kinds, and unspellable trees raise ValueError.

import json
import carve

source = carve.render_ast_json(json.dumps({
    "type": "document",
    "srcByteLength": 0,
    "children": [{"type": "paragraph", "children": [
        {"type": "text", "value": "*literal text*"}
    ]}]
}))

Docling conversion is maintained in the separate docling-carve package.