Understanding Python Automation Scripts for Junos Devices

Python Scripts Overview

As an alternative to SLAX and XSLT, you can create and execute Python scripts on Junos devices that support the Python extensions package in the software image. Python is a practical, feature-rich language with extensive library support that enables you to create custom scripts. Table 1 outlines the Python versions available on Junos devices and notes the release in which support for that version was added or removed for certain types of scripts.

Python scripts can leverage all of the features and constructs in the Python language, which provides flexibility over SLAX and XSLT and enables you to perform operations that are difficult or impossible to perform in SLAX and XSLT. SLAX and XSLT are designed for processing XML data, but Python is suited for processing any format. Python supports an extensive list of data types, including lists, dictionaries, sets, and tuples, and many Python variables are mutable, unlike many SLAX and XSLT variables. SLAX and XSLT scripts have limited loop control, but Python scripts can utilize statements like break and continue to precisely control loop behavior. Python also has extensive support for file operations, and you can invoke the standard Python debugger on the command line to debug Python op scripts..

In addition, Junos OS supports the following in Python scripts:

• Junos PyEZ library—simplifies executing RPCs and performing operational and configuration tasks on devices running Junos OS.

• lxml library—simplifies XPath handling.

• Jinja2 library—template engine that enables you to generate content from predefined templates, which can be useful for generating Junos OS configuration data.

• IPv6—Starting in Junos OS Release 19.3R1, devices running Junos OS with upgraded FreeBSD support using IPv6 in Python automation scripts. For more information see IPv6 Support in Python Automation Scripts.

• Non-default routing instances—Starting in Junos OS Release 19.3R1, Python scripts on supported devices can use the set_routing_instance() extension function to connect to a remote device through a nondefault routing instance.

• Additional Python modules—For information about the modules that are available to Python scripts on devices running Junos OS, see Overview of Python Modules on Junos Devices.

To prevent the execution of unauthorized Python code on devices running Junos OS, unsigned Python scripts must meet certain requirements before you can execute the script on a device. For detailed information about the requirements for executing Python automation scripts on devices running Junos OS, see Requirements for Executing Python Automation Scripts on Junos Devices.

To execute unsigned Python scripts using either Python 2.7 or Python 3, you must configure the language python or language python3 statement, respectively, at the [edit system scripts] hierarchy level. If you configure the language python3 statement, the device uses Python 3 to execute scripts that support this Python version, and it uses Python 2.7 to execute scripts that do not support Python 3 in the given Junos OS release, as noted in Table 1.

For JET scripts, you must configure the version of the statement that corresponds to the Python version the script supports. For example, if you configure the language python3 statement for a JET script that only supports Python 2.7, you will receive a runtime error when you execute the script.

Python Script Inputs for Commit, Event, Op, and SNMP Scripts

Devices running Junos OS that support Python automation scripts include the following modules, which you can import into commit, event, op, and SNMP scripts:

• jcs module—provides access to a subset of the extension functions and templates that are available to SLAX and XSLT scripts.

  For information about Junos OS extension functions and templates, see Understanding Extension Functions in Junos OS Automation Scripts and Understanding Named Templates in Junos OS Automation Scripts.

• junos module—contains the Junos class and script inputs outlined in Table 2.

For detailed information about the different script inputs and how to import and use them in automation scripts, see:

• Global Parameters and Variables in Junos OS Automation Scripts

• Required Boilerplate for Commit Scripts

• Required Boilerplate for Op Scripts

• Required Boilerplate for Event Scripts

• Use Event and Remote Execution Details in Event Scripts

• Required Boilerplate for SNMP Scripts

Python Script Resources

Table 3 provides resources to help you create and execute Python scripts on devices running Junos OS. Table 4 provides resources for each of the different types of scripts.