Part 4 — Python for Network Automation (Beginner-Friendly)

Removing the Fear of Coding

Many network engineers have never written code beyond bash scripts. The thought of “becoming a programmer” feels daunting. Here’s the reality: you don’t need to be a programmer to write effective network automation. You need to understand basic programming concepts and know the libraries that exist.

Python Basics for Networking

Why Python specifically? Python’s syntax closely resembles English and requires minimal boilerplate compared to many other languages.

Fundamental Concepts (Network Context):

Variables, lists, dictionaries, loops, and conditionals are the building blocks:

router_ip = "192.168.1.1"
username = "admin"
password = "cisco123"

routers = ["192.168.1.1", "192.168.2.1", "192.168.3.1"]

device = {
  "host": "192.168.1.1",
  "username": "admin",
  "password": "cisco123",
  "device_type": "cisco_ios"
}

for router in routers:
  # connect to router and run commands
  pass

if device_uptime < 1000:
  alert("Device rebooted!")

Netmiko: SSH Automation Library

Netmiko abstracts SSH complexity, handling device prompts, command execution, and response parsing, making multi-device SSH automation trivial.

from netmiko import ConnectHandler

device = {
  "device_type": "cisco_ios",
  "host": "192.168.1.1",
  "username": "admin",
  "password": "password"
}

connection = ConnectHandler(**device)
routes = connection.send_command("show ip route")
print(routes)
connection.disconnect()

NAPALM: Multi-Vendor Abstraction

NAPALM provides vendor-agnostic getters and configuration helpers:

from napalm import get_network_driver

driver = get_network_driver("ios")
connection = driver("192.168.1.1", "admin", "password")
connection.open()
facts = connection.get_facts()
print(facts)

Practical Use Cases

Pre/Post Change Validation — gather baseline and compare after a change.

from netmiko import ConnectHandler

conn = ConnectHandler(**device)
routes_before = conn.send_command("show ip route")
# apply change
routes_after = conn.send_command("show ip route")
if routes_before != routes_after:
  print("⚠️ Routes changed!")

Automated Config Backup

from netmiko import ConnectHandler
from datetime import datetime
import os

devices = [{"device_type": "cisco_ios", "host": "10.1.1.1", "username": "admin", ...}]
backup_dir = f"backups/{datetime.now().strftime('%Y-%m-%d')}"
os.makedirs(backup_dir, exist_ok=True)

for device in devices:
  conn = ConnectHandler(**device)
  config = conn.send_command("show running-config")
  with open(f"{backup_dir}/{device['host']}.config", 'w') as f:
    f.write(config)
  conn.disconnect()

Automated Compliance Checks

from napalm import get_network_driver

def check_ntp_configured(device):
  driver = get_network_driver(device["os"])
  conn = driver(device["host"], device["user"], device["pass"])
  conn.open()
  config = conn.get_config()
  return "ntp" in config.lower()

Key Takeaway

Python for network automation is about knowing which libraries to use and getting comfortable with small, repeatable scripts that solve real problems.

Try this now: Write a short script that connects to one device with Netmiko, runs show version, and appends a line to devices_report.md with hostname and OS version.

Next: Part 5 — Ansible for network automation.