libyang

Python CFFI bindings to libyang.

Installation

pip install libyang

This assumes libyang.so is installed in the system and that libyang.h is available in the system include dirs.

You need the following system dependencies installed:

• Python development headers
• GCC
• Python CFFI module

On a Debian/Ubuntu system::

sudo apt-get install python3-dev gcc python3-cffi

Compilation Flags

If libyang headers and libraries are installed in a non-standard location, you can specify them with the LIBYANG_HEADERS and LIBYANG_LIBRARIES variables. Additionally, for finer control, you may use LIBYANG_EXTRA_CFLAGS and LIBYANG_EXTRA_LDFLAGS:

LIBYANG_HEADERS=/home/build/opt/ly/include \
LIBYANG_LIBRARIES=/home/build/opt/ly/lib \
LIBYANG_EXTRA_CFLAGS="-O3" \
LIBYANG_EXTRA_LDFLAGS="-rpath=/opt/ly/lib" \
       pip install libyang

Embedding libyang.so

If libyang headers and libraries are not installed on the system, you may build libyang.so and embed it into the libyang package before linking the CFFI extension against it (with a custom RPATH).

To do so, you must export the LIBYANG_INSTALL=embed variable when running pip:

LIBYANG_INSTALL=embed pip install libyang

This requires additional system dependencies in order to build the libyang C code:

• cmake
• Lib PCRE development headers

On a Debian/Ubuntu system:

sudo apt-get install cmake build-essential libpcre3-dev

Examples

Schema Introspection

>>> import libyang
>>> ctx = libyang.Context('/usr/local/share/yang/modules')
>>> module = ctx.load_module('ietf-system')
>>> print(module.print_mem('tree'))
module: ietf-system
  +--rw system
  |  +--rw contact?          string
  |  +--rw hostname?         ietf-inet-types:domain-name
  |  +--rw location?         string
  |  +--rw clock
  |  |  +--rw (timezone)?
  |  |     +--:(timezone-utc-offset)
  |  |        +--rw timezone-utc-offset?   int16
  |  +--rw dns-resolver
  |     +--rw search*    ietf-inet-types:domain-name
  |     +--rw server* [name]
  |     |  +--rw name          string
  |     |  +--rw (transport)
  |     |     +--:(udp-and-tcp)
  |     |        +--rw udp-and-tcp
  |     |           +--rw address    ietf-inet-types:ip-address
  |     +--rw options
  |        +--rw timeout?    uint8 <5>
  |        +--rw attempts?   uint8 <2>
  +--ro system-state
     +--ro platform
     |  +--ro os-name?      string
     |  +--ro os-release?   string
     |  +--ro os-version?   string
     |  +--ro machine?      string
     +--ro clock
        +--ro current-datetime?   ietf-yang-types:date-and-time
        +--ro boot-datetime?      ietf-yang-types:date-and-time

  rpcs:
    +---x set-current-datetime
    |  +---- input
    |     +---w current-datetime    ietf-yang-types:date-and-time
    +---x system-restart
    +---x system-shutdown

>>> xpath = '/ietf-system:system/ietf-system:dns-resolver/ietf-system:server'
>>> dnsserver = next(ctx.find_path(xpath))
>>> dnsserver
<libyang.schema.SList: server [name]>
>>> print(dnsserver.description())
List of the DNS servers that the resolver should query.

When the resolver is invoked by a calling application, it
sends the query to the first name server in this list.  If
no response has been received within 'timeout' seconds,
the resolver continues with the next server in the list.
If no response is received from any server, the resolver
continues with the first server again.  When the resolver
has traversed the list 'attempts' times without receiving
any response, it gives up and returns an error to the
calling application.

Implementations MAY limit the number of entries in this
list.
>>> dnsserver.ordered()
True
>>> for node in dnsserver:
...     print(repr(node))
...
<libyang.schema.SLeaf: name string>
<libyang.schema.SContainer: udp-and-tcp>
>>> ctx.destroy()
>>>

Data Tree

>>> import libyang
>>> ctx = libyang.Context()
>>> module = ctx.parse_module_str('''
... module example {
...   namespace "urn:example";
...   prefix "ex";
...   container data {
...     list interface {
...       key name;
...       leaf name {
...         type string;
...       }
...       leaf address {
...         type string;
...       }
...     }
...     leaf hostname {
...       type string;
...     }
...   }
... }
... ''')
>>> print(module.print_mem('tree'))
module: example
  +--rw data
     +--rw interface* [name]
     |  +--rw name       string
     |  +--rw address?   string
     +--rw hostname?    string

>>> node = module.parse_data_dict({
...     'data': {
...         'hostname': 'foobar',
...         'interface': [
...             {'name': 'eth0', 'address': '1.2.3.4/24'},
...             {'name': 'lo', 'address': '127.0.0.1'},
...         ],
...     },
... })
>>> print(node.print_mem('xml', pretty=True))
<data xmlns="urn:example">
  <interface>
    <name>eth0</name>
    <address>1.2.3.4/24</address>
  </interface>
  <interface>
    <name>lo</name>
    <address>127.0.0.1</address>
  </interface>
  <hostname>foobar</hostname>
</data>

>>> node.print_dict()
{'data': {'interface': [{'name': 'eth0', 'address': '1.2.3.4/24'}, {'name': 'lo', 'address': '127.0.0.1'}], 'hostname': 'foobar'}}
>>> node.free()
>>> ctx.destroy()
>>>

See tests for more examples.