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============================= YANG Development Kit (Python)

.. contents:: Table of Contents

Overview

The YANG Development Kit (YDK) is a Software Development Kit that provides API's that are modeled in YANG. The main goal of YDK is to reduce the learning curve of YANG data models by expressing the model semantics in an API and abstracting protocol/encoding details.
YDK is composed of a core package that defines services and providers, plus one or more module bundles that are based on YANG models.

Backward Compatibility

The Python YDK-0.8.4 core package is compatible with all model bundles generated previously with ydk-gen releases starting from 0.7.3. Please see the release notes <https://github.com/CiscoDevNet/ydk-py/releases/tag/0.8.4>_ for details.

Docker

A docker image <https://docs.docker.com/engine/reference/run/>_ is automatically built with the latest ydk-py installed. This be used to run ydk-py without installing anything natively on your machine.

To use the docker image, install docker <https://docs.docker.com/install/>_ on your system and run the below command. See the docker documentation <https://docs.docker.com/engine/reference/run/>_ for more details::

docker run -it ydkdev/ydk-py

System Requirements

Linux

Ubuntu (Debian-based)

The following packages must be present in your system before installing YDK-Py::

Install Third-party software

sudo apt-get install gdebi-core python3-dev python-dev libtool-bin
sudo apt-get install libcurl4-openssl-dev libpcre3-dev libssh-dev libxml2-dev libxslt1-dev cmake

Download and install YDK core library libydk. You can install the library using prebuilt debian packages for Xenial and Bionic LTS distributions. For other Ubuntu distributions it is recommended to build core library from source.

For Xenial (Ubuntu 16.04.4)::

Upgrade compiler to gcc 5.*

sudo apt-get install gcc-5 g++-5 -y > /dev/null sudo ln -sf /usr/bin/gcc-5 /usr/bin/cc sudo ln -sf /usr/bin/g++-5 /usr/bin/c++

wget https://devhub.cisco.com/artifactory/debian-ydk/0.8.4/xenial/libydk-0.8.4-1.amd64.deb sudo gdebi libydk-0.8.4-1.amd64.deb

For Bionic (Ubuntu 18.04.1)::

wget https://devhub.cisco.com/artifactory/debian-ydk/0.8.4/bionic/libydk-0.8.4-1.amd64.deb sudo gdebi libydk-0.8.4-1.amd64.deb

Centos (Fedora-based)

The following packages must be present in your system before installing YDK-Py. Currently, only Centos7/RHEL7 are known to work::

Install Third-party software

sudo yum install epel-release sudo yum install libssh-devel gcc-c++ python-devel python3-devel

Upgrade compiler to gcc 5.*

sudo yum install centos-release-scl -y > /dev/null sudo yum install devtoolset-4-gcc* -y > /dev/null sudo ln -sf /opt/rh/devtoolset-4/root/usr/bin/gcc /usr/bin/cc sudo ln -sf /opt/rh/devtoolset-4/root/usr/bin/g++ /usr/bin/c++

Install YDK core library

sudo yum install https://devhub.cisco.com/artifactory/rpm-ydk/0.8.4/libydk-0.8.4-1.x86_64.rpm

MacOS

It is required to install Xcode command line tools, homebrew <http://brew.sh>_ and the following homebrew packages on your system before installing YDK-Py::

xcode-select --install /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)" brew install pkg-config libssh xml2 libxml2 curl pcre cmake pybind11 doxygen libgcrypt

curl -O https://devhub.cisco.com/artifactory/osx-ydk/0.8.4/libydk-0.8.4-Darwin.pkg sudo installer -pkg libydk-0.8.4-Darwin.pkg -target /

Libssh Installation

The libssh-0.8.0 does not support <http://api.libssh.org/master/libssh_tutor_threads.html>_ separate threading library, which is required for YDK. If after installation of libssh package the libssh_threads.a is missing, please downgrade the installation to libssh-0.7.6, or upgrade to libssh-0.8.1 or higher.

Note for MacOS Before installing libssh make sure the environment for openssl is setup::

brew reinstall openssl export OPENSSL_ROOT_DIR=/usr/local/opt/openssl

Download libssh-0.7.6 source code, compile it and install::

wget https://git.libssh.org/projects/libssh.git/snapshot/libssh-0.7.6.tar.gz tar zxf libssh-0.7.6.tar.gz && rm -f libssh-0.7.6.tar.gz mkdir libssh-0.7.6/build && cd libssh-0.7.6/build cmake .. sudo make install

gNMI Requirements

In order to enable YDK support for gNMI protocol, which is optional, the following third party software must be installed prior to gNMI YDK component installation.

Install protobuf and protoc

.. code-block:: sh

  wget https://github.com/google/protobuf/releases/download/v3.5.0/protobuf-cpp-3.5.0.zip
  unzip protobuf-cpp-3.5.0.zip
  cd protobuf-3.5.0
  ./configure
  make
  sudo make install
  sudo ldconfig

Install gRPC
~~~~~~~~~~~~

.. code-block:: sh

  git clone -b v1.9.1 https://github.com/grpc/grpc
  cd grpc
  git submodule update --init
  make
  sudo make install
  sudo ldconfig

Instal YDK gNMI library
~~~~~~~~~~~~~~~~~~~~~~~

**Ubuntu**

For Xenial (Ubuntu 16.04.4)::

  wget https://devhub.cisco.com/artifactory/debian-ydk/0.8.4/xenial/libydk_gnmi-0.4.0-4.amd64.deb
  sudo gdebi libydk_gnmi-0.4.0-4.amd64.deb

For Bionic (Ubuntu 18.04.1)::

  wget https://devhub.cisco.com/artifactory/debian-ydk/0.8.4/bionic/libydk_gnmi-0.4.0-4.amd64.deb
  sudo gdebi libydk_gnmi-0.4.0-4.amd64.deb

**CentOS**::

  sudo yum install https://devhub.cisco.com/artifactory/rpm-ydk/0.8.4/libydk_gnmi-0.4.0-4.x86_64.rpm

**MacOS**::

  curl -O https://devhub.cisco.com/artifactory/osx-ydk/0.8.4/libydk_gnmi-0.4.0-4.Darwin.pkg
  sudo installer -pkg libydk_gnmi-0.4.0-4.Darwin.pkg -target /

Runtime environment
~~~~~~~~~~~~~~~~~~~

There is an open issue with gRPC on Centos/Fedora, which requires an extra step before running any YDK gNMI application. 
See this issue on `GRPC GitHub <https://github.com/grpc/grpc/issues/10942#issuecomment-312565041>`_ for details. 
As a workaround, the YDK based application runtime environment must include setting of `LD_LIBRARY_PATH` variable::

  PROTO="/Your-Protobuf-and-Grpc-installation-directory"
  export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$PROTO/grpc/libs/opt:$PROTO/protobuf-3.5.0/src/.libs:/usr/local/lib64

Python Requirements
-------------------

YDK supports both Python2 and Python3 versions. At least Python2.7 or Python3.4 must be installed on your system.

It is also required for Python installation to include corresponding shared library. As example::

  python2.7  - /usr/lib/x86_64-linux-gnu/libpython2.7.so
  python3.5m - /usr/lib/x86_64-linux-gnu/libpython3.5m.so

Please follow `System Requirements`_ to assure presence of shared Python libraries.

If you choose to install Python from source (need specific version), please include `--enable-shared` flag in `configure`
command to include build of shared library::

  cd Python3.4.1
  ./configure --prefix=/opt/python --enable-shared
  make
  make install

Here the `/opt/python` is your Python installation directory. If installation directory is different from the system path,
you need to configure `CMAKE_LIBRARY_PATH` environment variable to assure that `cmake` uses correct Python library::

  export CMAKE_LIBRARY_PATH=/opt/python/lib

Run `pip install ydk` command with `-v` option and in the console output note location of found `PythonLibs`.
Make sure it matches with your installed Pyton dynamic library location::

  -- Found PythonLibs: /opt/python/lib/libpython3.4m.so

In some OS configurations during YDK package installation the cmake fails to find C/C++ headers for previously installed YDK libraries.
In this case the header location must be specified explicitly (in below commands the default location is shown)::

  export C_INCLUDE_PATH=/usr/local/include
  export CPLUS_INCLUDE_PATH=/usr/local/include

Mac OS
~~~~~~

The developers of Python2 on Mac OS might face an `installation issue <https://github.com/CiscoDevNet/ydk-gen/issues/837>`_.
This is well known and documented issue. Each developer might have different approaches for its resolution.
One of them is to use Python2 virtual environment. See section `Using Python virtual environment`_ for details.

In addition it is required properly set `CMAKE_LIBRARY_PATH` environment variable to assure that `cmake` uses correct Python library.
Follow these steps to find and set correct library path.

1. Find installations of `libpython2.7` library:

.. code-block:: sh

  locate libpython2.7.dylib
  /System/Library/Frameworks/Python.framework/Versions/2.7/lib/libpython2.7.dylib
  /System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/config/libpython2.7.dylib
  /usr/lib/libpython2.7.dylib
  /usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/libpython2.7.dylib
  /usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/config/libpython2.7.dylib

2. Choose non-system Python library installation and set `CMAKE_LIBRARY_PATH` before any YDK component installation. Example:

.. code-block:: sh

  export CMAKE_LIBRARY_PATH=/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib

3. Run YDK core package installation with '-v' flag to check that `PythonLibs` points to correct library path. Example:

.. code-block:: sh

  $ ./generate.py --core
  $ pip install -v gen-api/python/ydk/dist/ydk*.tar.gz
  
4. In 'cmake' log look for 'PythonLibs' and 'found version' settings line:
  
.. code-block:: sh

  -- Found PythonLibs: /usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/libpython2.7.dylib (found version "2.7.15")
  
5. Finally test you YDK core library installation from CLI, making sure there are no errors:

.. code-block:: sh

  $ python -c "import ydk.types"


How to install
==============

Using Python virtual environment
--------------------------------

You may want to perform the installation under Python virtual environment (`virtualenv <https://pypi.python.org/pypi/virtualenv/>`_/`virtualenvwrapper  <https://pypi.python.org/pypi/virtualenvwrapper>`_).  
The virtual environment allows you to install multiple versions of YDK if needed.  In addition, it prevents any potential conflicts between package dependencies in your system.

To install virtual environment support in your system, execute::

  pip install virtualenv virtualenvwrapper
  source /usr/local/bin/virtualenvwrapper.sh

To create and activate new virtual environment::

  mkvirtualenv -p python2.7 ydk-py
  
To activate existing virtual environment::

  source ~/.virtualenvs/py2/bin/activate
  
To exit virtual environment::

  deactivate

Once Python virtual environment is activated, you can perform quick installation or installation from source described above. 
Take into consideration that you must not attempt to install YDK as root user under virtual environment.

Quick Install
-------------

You can install the latest model packages from the Python package index.  Note that, in some systems, you need to install the new package as root.  
You get a fully operational YDK environment by installing the ``cisco-ios-xr`` and/or ``cisco-ios-xe`` bundle(s) (depending on whether you're developing for an IOS XR or IOS XE platform), 
which automatically installs all other YDK-related packages (``ydk``, ``openconfig`` and ``ietf`` packages)::

  pip install ydk-models-cisco-ios-xr
  pip install ydk-models-cisco-ios-xe

Alternatively, you can perform a partial installation.  If you only want to instal