libyang-python

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
• FFI development headers

On a Debian/Ubuntu system:

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

Compatibility

The current version requires at least C libyang 2.25.

The last version of the bindings that works with C libyang 1.x is v1.7.0.

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

Examples

Schema Introspection

>>> import libyang
>>> ctx = libyang.Context('/usr/local/share/yang/modules')
>>> module = ctx.load_module('ietf-system')
>>> print(module)
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 the tests folder for more examples.

Contributing

This is an open source project and all contributions are welcome.

Issues

Please create new issues for any bug you discover at https://github.com/CESNET/libyang-python/issues/new. It is not necessary to file a bug if you are preparing a patch.

Pull Requests

Here are the steps for submitting a change in the code base:

1. Fork the repository: https://github.com/CESNET/libyang-python/fork

2. Clone your own fork into your development machine:

   git clone https://github.com/<you>/libyang-python
   

3. Create a new branch named after what your are working on:

   git checkout -b my-topic -t origin/master
   

4. Edit the code and call make format to ensure your modifications comply with the coding style.

   Your contribution must be licensed under the MIT License . At least one copyright notice is expected in new files.

5. If you are adding a new feature or fixing a bug, please consider adding or updating unit tests.

6. Before creating commits, run make lint and make tests to check if your changes do not break anything. You can also run make which will run both.

7. Once you are happy with your work, you can create a commit (or several commits). Follow these general rules:

   • Address only one issue/topic per commit.
   • Describe your changes in imperative mood, e.g. "make xyzzy do frotz" instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy to do frotz", as if you are giving orders to the codebase to change its behaviour.
   • Limit the first line (title) of the commit message to 60 characters.
   • Use a short prefix for the commit title for readability with git log --oneline. Do not use the fix: nor feature: prefixes. See recent commits for inspiration.
   • Only use lower case letters for the commit title except when quoting symbols or known acronyms.
   • Use the body of the commit message to actually explain what your patch does and why it is useful. Even if your patch is a one line fix, the description is not limited in length and may span over multiple paragraphs. Use proper English syntax, grammar and punctuation.
   • If you are fixing an issue, use appropriate Closes: <URL> or Fixes: <URL> trailers.
   • If you are fixing a regression introduced by another commit, add a Fixes: <COMMIT_ID> ("<TITLE>") trailer.
   • When in doubt, follow the format and layout of the recent existing commits.
   • The following trailers are accepted in commits. If you are using multiple trailers in a commit, it's preferred to also order them according to this list.
     • Closes: <URL>: close the referenced issue or pull request.
     • Fixes: <SHA> ("<TITLE>"): reference the commit that introduced a regression.
     • Link: <URL>: any useful link to provide context for your commit.
     • Suggested-by
     • Requested-by
     • Reported-by
     • Co-authored-by
     • Tested-by
     • Reviewed-by
     • Acked-by
     • Signed-off-by: Compulsory!

   There is a great reference for commit messages in the Linux kernel documentation.

   IMPORTANT: you must sign-off your work using git commit --signoff. Follow the Linux kernel developer's certificate of origin for more details. All contributions are made under the MIT license. If you do not want to disclose your real name, you may sign-off using a pseudonym. Here is an example:

   Signed-off-by: Robin Jarry <robin@jarry.cc>
   

8. Push your topic branch in your forked repository:

   git push origin my-topic
   

   You should get a message from Github explaining how to create a new pull request.

9. Wait for a reviewer to merge your work. If minor adjustments are requested, use git commit --fixup $sha1 to make it obvious what commit you are adjusting. If bigger changes are needed, make them in new separate commits. Once the reviewer is happy, please use git rebase --autosquash to amend the commits with their small fixups (if any), and git push --force on your topic branch.

Thank you in advance for your contributions!