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Opinionated Python bindings for the libyang library

Project description

Opinionated Python bindings for the libyang library

Install via pip Python versions GitHub Workflow Status

Python bindings and packaging of libyang. We're focusing on parsing, validating and accessing YANG-modeled JSON data trees. Essentially, just enough to get gnpy going. Want more? Patches welcome.

Compared to the CFFI libyang bindings, this wrapper takes care of low-level memory management. This means no more and ctx.destroy(). We also produce prebuilt binary wheels to make installation very simple.


Loading YANG data

import oopt_gnpy_libyang as ly

c = ly.Context('tests/yang', ly.ContextOptions.AllImplemented | ly.ContextOptions.NoYangLibrary)
for m in ('iana-if-type', 'ietf-interfaces', 'ietf-ip'):
blob = '''{
  "ietf-interfaces:interfaces": {
    "interface": [
        "name": "lo",
        "type": "iana-if-type:softwareLoopback",
        "ietf-ip:ipv4": {
          "address": [
              "ip": "",
              "prefix-length": 8
        "ietf-ip:ipv6": {
          "address": [
              "ip": "::1",
              "prefix-length": 128
        "name": "eth0",
        "type": "iana-if-type:ethernetCsmacd"

data = c.parse_data_str(blob,
    ly.DataFormat.JSON, ly.ParseOptions.Strict | ly.ParseOptions.Ordered,
    ly.ValidationOptions.Present | ly.ValidationOptions.NoState)

Working with data

Libyang works with forests (sets of trees), this is how to process all the data:

for x in data.siblings():
    print(f'a sibling: {x.path}')
    for xx in x.childrenDfs():
        print(f' {"term " if xx.is_term else "child"}: {xx.path}')
        if xx.is_term:
            print(f'  {xx.as_term()} {" (default)" if xx.as_term().is_default_value else ""}')

Data can be accessed via their known paths, of course. Either as a full, multi-level XPath:

data["interface[name='lo']/ietf-ip:ipv6/address[ip='::1']/prefix-length"].as_term().value == 128

Or individually, one item per index:


Everything is an XPath, so it's possible to take a shortcut and skip specifying keys for single-element lists:

data["interface[name='lo']"]["ietf-ip:ipv6"]["address"]["prefix-length"].as_term().value == 128

The data are provided as native Python types:

    .as_term().value) == int

Validation errors

In libyang, if an operation fails, error details are available via context.errors():

import json
wrong = json.loads(blob)
    ["ietf-ip:ipv6"]["address"][0]["prefix-length"] = 666
    data = c.parse_data_str(json.dumps(wrong),
        ly.DataFormat.JSON, ly.ParseOptions.Strict | ly.ParseOptions.Ordered,
        ly.ValidationOptions.Present | ly.ValidationOptions.NoState)
    assert False
except ly.Error:
    for error in c.errors():
        assert error.path == "Schema location \"/ietf-interfaces:interfaces/interface/ietf-ip:ipv6/address/prefix-length\", data location \"/ietf-ip:address[ip='::1']\", line number 1."
        assert error.message == 'Value "666" is out of type uint8 min/max bounds.'


We're producing wheels for many popular platforms. The installation is as simple as:

$ pip install oopt-gnpy-libyang

Building from source

Since this library is a Python wrapper around a C++ wrapper around a C library, source-based builds are more complex. They require:

  • a C++20 compiler (e.g., GCC 10+, clang 10+, MSVC 17.2+)
  • libyang and its dependencies
  • libyang-cpp and its dependencies
  • CMake 3.21+

Unlike the wheels already bundle all the required libraries, when building from source, libyang, libyang-cpp and all their dependencies will have to be installed first. Also, in a from-source build these won't be bundled into the resulting package. For an inspiration, consult our GitHub packaging recipes.


Copyright © 2021-2022 Telecom Infra Project and GNPy contributors. Licensed under the 3-clause BSD license.

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