leptris (Python) — lxml-shaped bindings for libleptris

leptris wraps the libleptris C API (XML 1.0 parsing, XPath 1.0) using cffi in ABI mode. The Ruby binding mirrors Nokogiri; this binding mirrors lxml — parse, query, serialize code written against lxml's read path ports with an import change.

The pinned libleptris version lives in libleptris-version.txt (lockstep releases); CI builds it from the release tarball. The binding loads the shared library from LEPTRIS_LIB_PATH or the loader path.

Requirements

Python 3.9+
cffi (installed automatically)
libleptris as a shared library (libleptris.dylib / .so / .dll) on the loader path, or pointed to by LEPTRIS_LIB_PATH (which must name the library file — the loader dlopens it verbatim). For a development checkout:

cmake -B build -S /path/to/leptris -DLEPTRIS_BUILD_SHARED=ON
cmake --build build --target leptris_shared
export LEPTRIS_LIB_PATH=/path/to/leptris/build/src/libleptris.dylib

Quick start

from leptris import fromstring, tostring

root = fromstring("<library><book id='1' lang='en'>Ulysses</book></library>")

root.tag                                # "library"
root[0].get("id")                       # "1"
root[0].attrib                          # {"id": "1", "lang": "en"}
root[0].text                            # "Ulysses"

root.xpath("count(//book)")             # 1.0
[b.text for b in root.findall("book")]  # ["Ulysses"]

tostring(root[0], encoding="unicode")   # "<book id=\"1\" lang=\"en\">Ulysses</book>"

Documents own the tree; use the context manager or close():

from leptris import parse

with parse("catalog.xml") as doc:
    doc.xpath("//book[@lang='en']")

Namespaces, variables, canonical XML and streaming:

root.xpath("//x:item", namespaces={"x": "urn:ex"})
root.xpath("//book[@id=$id]", variables={"id": "2"})
c14n(root, exclusive=True)

from leptris import sax
sax.parse(xml, handler)                       # one-shot
with sax.StreamingParser(handler) as parser:  # push, constant memory
    parser.feed(chunk, final=last)

Migrating from lxml

lxml	leptris	Notes
`etree.fromstring` / `etree.XML`	`fromstring` / `XML`
`etree.parse`	`parse`	paths and file-likes; no URLs
`etree.tostring(elem, …)`	`tostring(elem, …)`	bytes by default, `encoding="unicode"` for str
`elem.tag` / `.text` / `.tail`	same	`tag` uses `{uri}local` Clark notation; CDATA merges into text (lxml's default parser behavior)
`elem.attrib` / `.get()` / `.keys()` / `.items()`	same	`attrib` is a read-only Mapping
`elem.getparent/getnext/getprevious`	same
`elem[i]`, `len(elem)`, iteration, slices	same	indexing is child indexing, never attribute lookup
`elem.iter()` / `.iterdescendants()` / `.itertext()`	same
`elem.find/findall/findtext`	same	accepts full XPath 1.0 — a superset of ElementPath — including `{uri}local` names
`elem.xpath(expr, namespaces=…)`	same	plus `variables={…}` (leptris extension)
`etree.c14n` / `etree.XInclude`	`c14n(…)` / `doc.process_xinclude()`
`etree.XMLSyntaxError`	`ParseError`	XPath failures raise `XPathError`; both subclass `LeptrisError`
`etree.Element`, `SubElement`, `append`, `set`, `remove`	absent	libleptris is a read-only parser; build trees elsewhere
`etree.iterparse`	absent	use `leptris.sax.StreamingParser` (callback-based, constant memory)
smart strings	plain `str`	XPath string/attribute results
`elem.nsmap`	absent	use `elem.namespace` / `elem.prefix` and `xpath(namespaces=…)`
`etree.XPath` compiled objects	absent	upstream ask: compiled-expression C API
parser options (`resolve_entities`, …)	absent	libleptris 1.2.0 has no per-parse options
`elem.sourceline`	absent	upstream ask: node positions
undeclared XPath prefix	raises in lxml	evaluates to an empty nodeset here

Layout

leptris/_ffi.py — cdef mirror of the public headers + loader (the only place C is touched)
leptris/element.py, document.py, node.py, xpath.py — lxml-compatible wrappers; node.py exposes the full DOM (comments, CDATA, PIs) beneath the ElementTree-shaped surface
leptris/api.py — fromstring/parse/tostring/c14n
leptris/sax.py — SAX one-shot and streaming
tests/ — pytest suite (pytest with LEPTRIS_LIB_PATH set)
benchmarks/ — matrix vs lxml/ElementTree/minidom (pip install .[bench], then python -m benchmarks.matrix)

Memory model

The Document owns the whole tree and its pool. Accessor strings are copied into Python str at the boundary, so nothing depends on document lifetime after a call returns. Elements keep a reference to their Document, so the pool cannot be freed while any wrapper is alive. Prefer explicit close() / the context manager; __del__ is a refcounting safety net, not a contract. Using an element after its document is closed raises LeptrisError.

Versioning

libleptris-version.txt pins the library release the binding is built and tested against. From 1.3.0 the package follows its own semver: 1.2.0 shipped an interim bespoke API to no adopters, and 1.3.0 replaces it with the lxml-shaped API (breaking, but pre-adoption). pyproject.toml and leptris/__init__.py must agree at release time.

Publishing

Releases publish to PyPI via .github/workflows/release.yml, using PyPI trusted publishing (no stored credentials). The workflow runs on manual dispatch (ships the version in pyproject.toml) and is called by the libleptris release flow (publish: true), so every libleptris release ships the wheel.

Local development

python3 -m venv .venv
./.venv/bin/pip install --upgrade build pytest cffi
./.venv/bin/pip install -e .[test,bench]
LEPTRIS_LIB_PATH=/path/to/libleptris.dylib ./.venv/bin/python -m pytest tests/ -q

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