Device lists, for loops, find_prompt & collecting results
Many devices, one loop
Lesson 2 of 20 · 12 min · Module 1: First steps with automation
The point of automation is doing the same thing on many devices. A list of devices and a for loop turn one login into fifty.
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By the end, you’ll be able to…
- Loop over a list of devices
- Read who answered from the prompt
- Collect results in a dictionary
The idea
Keep the devices in a list and build each Netmiko dictionary inside the loop. Collect what you learn in a dictionary keyed by device, so the results stay together. find_prompt() shows who answered: Cisco prints sw1#, Huawei prints <sw3> in user view. strip() with a set of characters removes them from both ends.
for host in ["10.0.0.11", "10.0.0.12"]:
device = {"device_type": "cisco_ios", "host": host,
"username": USERNAME, "password": PASSWORD}
with ConnectHandler(**device) as conn:
print(host, conn.find_prompt())01Two vendors, two prompts
The same method works on both vendors; only the device_type differs. Notice the prompts: sw1# on Cisco, <sw3> on Huawei.
import os
from netmiko import ConnectHandler
USERNAME = os.environ["NET_USERNAME"]
PASSWORD = os.environ["NET_PASSWORD"]
for host, device_type in [("10.0.0.11", "cisco_ios"), ("10.0.0.13", "huawei")]:
device = {"device_type": device_type, "host": host,
"username": USERNAME, "password": PASSWORD}
with ConnectHandler(**device) as conn:
print(conn.find_prompt())sw1#
<sw3>02Strip the symbols
strip("#<>") removes any of those characters from both ends of the string, and nothing from the middle.
print("sw1#".strip("#<>"))
print("<sw3>".strip("#<>"))sw1
sw303One dictionary for the results
Assigning to results[key] inside the loop builds the dictionary step by step. Printing it at the end shows everything at once.
results = {}
for host in ["10.0.0.11", "10.0.0.12"]:
results[host] = "checked"
print(results){'10.0.0.11': 'checked', '10.0.0.12': 'checked'}Your turn
switches (the last one is a Huawei device) and build hostnames, a dictionary that maps each address to the hostname shown in its prompt, without #, < or >. Print it.What the checks look for
- hostnames maps every address to its name
- Logged in to all four switches
- The result is printed
- The password is not written in the code
Take this with you
Put devices in a list, loop over it, and collect the results in a dictionary keyed by device.
Go a little further
Netmiko also keeps the hostname in conn.base_prompt. Use it instead of strip() and check that you get the same dictionary.