Opinionated Python bindings for the libyang library
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 node.free() and ctx.destroy().
We also produce prebuilt binary wheels to make installation very simple.
Usage
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'):
c.load_module(m)
blob = '''{
"ietf-interfaces:interfaces": {
"interface": [
{
"name": "lo",
"type": "iana-if-type:softwareLoopback",
"ietf-ip:ipv4": {
"address": [
{
"ip": "127.0.0.1",
"prefix-length": 8
}
]
},
"ietf-ip:ipv6": {
"address": [
{
"ip": "::1",
"prefix-length": 128
}
]
}
},
{
"name": "eth0",
"type": "iana-if-type:ethernetCsmacd"
}
]
}
}'''
data = c.parse_data(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.children_dfs():
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 == 128Or individually, one item per index:
data["interface[name='lo']"]["ietf-ip:ipv6"]["address[ip='::1']"]["prefix-length"].as_term().valueEverything 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 == 128The data are provided as native Python types:
type(data["interface[name='lo']"]["ietf-ip:ipv6"]["address"]["prefix-length"]
.as_term().value) == intAbsolute paths and generic XPath expressions can be used to retrieve arbitrary parts of the data forest, and to iterate over them:
for iface in data.find("/ietf-interfaces:interfaces/interface"):
print iface["name"].as_term().valueRelative XPath conditions can be also used at the root level (which is represented as NULL in the C level):
for iface in search_at_root(data)("ietf-interfaces:interfaces/interface"):
print iface["name"].as_term().valueNew values can be created; use None for non-terminals, or str when a value is needed:
node = ctx.create("/ietf-interfaces:interfaces/interface[name='666']")
another = ctx.create("/ietf-interfaces:interfaces/interface[name='666']/ietf-ip:ipv6/enabled", "true")
data["interface[name='lo']"]["ietf-ip:ipv6"]["address"]["prefix-length"] = "64"Validation errors
In libyang, if an operation fails, error details are available via context.errors():
import json
wrong = json.loads(blob)
wrong["ietf-interfaces:interfaces"]["interface"][0]\
["ietf-ip:ipv6"]["address"][0]["prefix-length"] = 666
try:
data = c.parse_data(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.'Installing
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+)
-
libyangand its dependencies -
libyang-cppand 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.
License
Copyright © 2021-2023 Telecom Infra Project and GNPy contributors. Licensed under the 3-clause BSD license.
