Putting It All Together: The Complete Project

import csv
import json


def is_valid_device(device):
  """A device record needs at least a hostname and an IP to be usable."""
  return bool(device.get("hostname")) and bool(device.get("ip"))


def simulate_connection(device):
  """
  Stands in for a real SSH connection — this exact function is what
  gets replaced with a real Netmiko call in the next module. Returns
  the device's current NTP and VLAN compliance state, or raises
  ConnectionError if the device can't be reached.
  """
  simulated_state = {
      "SW1": {"reachable": True, "ntp_synced": True, "vlan_compliant": True},
      "SW2": {"reachable": True, "ntp_synced": False, "vlan_compliant": True},
      "SW3": {"reachable": False, "ntp_synced": None, "vlan_compliant": None},
  }

  state = simulated_state.get(device["hostname"])

  if state is None or not state["reachable"]:
      raise ConnectionError(f"{device['hostname']} is unreachable")

  return state


def check_compliance(state):
  """Turn a device's raw state into a plain-language compliance status."""
  if state["ntp_synced"]:
      if state["vlan_compliant"]:
          return "compliant"
      else:
          return "vlan non-compliant"
  else:
      return "ntp non-compliant"


# --- Load and validate inventory ---
with open("devices.csv") as f:
  devices = list(csv.DictReader(f))

valid_devices = []
for device in devices:
  if is_valid_device(device):
      valid_devices.append(device)
  else:
      print(f"Skipping invalid inventory record: {device}")

# --- Process every device ---
results = []

for device in valid_devices:
  print(f"Checking {device['hostname']}...")

  try:
      state = simulate_connection(device)
  except ConnectionError:
      print(f"{device['hostname']}: unreachable")
      results.append({
          "hostname": device["hostname"],
          "ip": device["ip"],
          "status": "unreachable",
      })
      continue

  status = check_compliance(state)
  print(f"{device['hostname']}: {status}")
  results.append({
      "hostname": device["hostname"],
      "ip": device["ip"],
      "status": status,
  })

# --- Write the report ---
with open("compliance_report.json", "w") as f:
  json.dump(results, f, indent=4)

# --- Terminal summary ---
compliant = 0
needs_attention = 0
for result in results:
  if result["status"] == "compliant":
      compliant += 1
  else:
      needs_attention += 1

print()
print("--- Summary ---")
print(f"Checked:         {len(results)} devices")
print(f"Compliant:       {compliant}")
print(f"Needs attention: {needs_attention}")
print("Report written to compliance_report.json")

Save this as network_health_check.py alongside devices.csv and run 'python network_health_check.py' — no installs, no real switches.

hostname,ip,platform
SW1,10.10.10.1,cisco_ios
SW2,10.10.10.2,cisco_ios
SW3,10.10.10.3,cisco_ios

The same three-device inventory used throughout this module — SW1 fully healthy, SW2 reachable but out of NTP sync, SW3 unreachable.

Checking SW1...
SW1: compliant
Checking SW2...
SW2: ntp non-compliant
Checking SW3...
SW3: unreachable

--- Summary ---
Checked:         3 devices
Compliant:       1
Needs attention: 2
Report written to compliance_report.json

One 'Checking...' / result line per device, then a short summary — three checked, one fully compliant, two needing attention (SW2's NTP drift, SW3 being down).

[
  {
      "hostname": "SW1",
      "ip": "10.10.10.1",
      "status": "compliant"
  },
  {
      "hostname": "SW2",
      "ip": "10.10.10.2",
      "status": "ntp non-compliant"
  },
  {
      "hostname": "SW3",
      "ip": "10.10.10.3",
      "status": "unreachable"
  }
]

Every device from the inventory has exactly one entry — nothing silently dropped, every status traceable back to what simulate_connection() and check_compliance() actually decided for it.