Use Junos PyEZ to Retrieve Facts from Junos Devices

Junos PyEZ is a microframework for Python that enables you to manage and automate Junos devices. Junos PyEZ models each device as an instance of the jnpr.junos.device.Device class. After connecting to a Junos device, Junos PyEZ applications can retrieve facts about the device. The device facts are accessed as the facts attribute of the Device object. For detailed information about the keys that are included in the returned device facts, see jnpr.junos.facts.

The following example establishes a NETCONF session over SSH with the device and prints the device facts. The device uses SSH keys to authenticate the user.

from jnpr.junos import Device
from pprint import pprint

with Device(host='router1.example.net') as dev:
    pprint (dev.facts['hostname'])
    pprint (dev.facts)

user1@server:~$ python3 get-facts.py
'router1'
{'2RE': True,
 'HOME': '/var/home/user1',
 'RE0': {'last_reboot_reason': '0x200:normal shutdown',
         'mastership_state': 'master',
         'model': 'RE-MX-104',
         'status': 'OK',
         'up_time': '25 days, 8 hours, 22 minutes, 40 seconds'},
 'RE1': {'last_reboot_reason': '0x200:normal shutdown',
         'mastership_state': 'backup',
         'model': 'RE-MX-104',
         'status': 'OK',
         'up_time': '25 days, 8 hours, 23 minutes, 55 seconds'},
 ...

In Junos PyEZ Release 2.0.0 and earlier releases, when the application calls the Device open() method to connect to a device, Junos PyEZ automatically gathers the device facts for NETCONF-over-SSH connections and gathers the device facts for Telnet and serial console connections when you explicitly include gather_facts=True in the Device argument list.

Starting in Junos PyEZ Release 2.1.0, device facts are gathered on demand for all connection types. Each fact is gathered and cached the first time the application accesses its value or the value of a dependent fact. When you print or use device facts, previously accessed facts are served from the cache, and facts that have not yet been accessed are retrieved from the device. If a fact is not supported on a given platform, or if the application encounters an issue gathering the value of a specific fact, then the value of that fact is None.

Junos PyEZ caches a device fact when it first accesses the fact or a dependent fact, but it does not update the cached value upon subsequent access. To refresh the device facts, call the facts_refresh() method. The facts_refresh() method empties the cache of all facts, such that when the application next accesses a fact, it retrieves it from the device and stores the current value in the cache.

from jnpr.junos import Device
from pprint import pprint

with Device(host='router1.example.net') as dev:
    pprint (dev.facts)
    dev.facts_refresh()
    pprint (dev.facts)

To refresh only a single fact or a set of facts, include the keys argument in the facts_refresh() method, and specify the keys to clear from the cache. For example:

dev.facts_refresh(keys='hostname')
dev.facts_refresh(keys=('hostname','domain','master'))

By default, Junos PyEZ returns the device facts as a dictionary-like object. Starting in Junos PyEZ Release 2.2.1, you can view the device facts in JavaScript Object Notation (JSON). To view a JSON representation of the facts, import the json module, and call the json.dumps() function.

from jnpr.junos import Device
import json

with Device(host='router1.example.net') as dev:
    print (json.dumps(dev.facts))