Unit 5 — Data Structures — Modeling Network Inventories

Units

✓ Whetting Your Appetite — Why Python for Networking? ✓ Using the Python Interpreter ✓ An Informal Introduction to Python — Network Basics ✓ Control Flow — Making Decisions in Network Scripts ✓ Data Structures — Modeling Network Inventories ✓ Modules — Organizing Your Network Scripts ✓ Input and Output — Reading and Writing Network Data ✓ Errors and Exceptions — Building Reliable Network Scripts ✓ Classes — Modeling Network Devices as Objects ✓ Standard Library Part I — Tools Every Network Script Needs ✓ Standard Library Part II — Logging, Formatting, and Counting ✓ Virtual Environments and Packages — Isolating Your Dependencies ✓ Capstone — Build a Network Inventory Tool

Lists in Depth

You have seen lists already. Now the full picture. Lists are ordered, mutable collections — you can add, remove, and reorder items.

devices = ["sw-core-01", "sw-access-01", "rtr-edge-01"]

devices.append("fw-dmz-01")    # add to end
devices.remove("rtr-edge-01")  # remove by value
devices.sort()                  # sort in place
print(devices)
# ['fw-dmz-01', 'sw-access-01', 'sw-core-01']

List comprehensions — build a filtered or transformed list in one line:

inventory = [
    {"name": "sw-core-01", "type": "switch"},
    {"name": "rtr-edge-01", "type": "router"},
    {"name": "sw-access-01", "type": "switch"},
]

switches = [d["name"] for d in inventory if d["type"] == "switch"]
# ['sw-core-01', 'sw-access-01']

Read it as: "give me the name of every device in inventory where the type is switch."

Tuples — Fixed Records

A tuple is like a list but immutable — once created, it cannot change. Use tuples for fixed records that should not be modified: a device's serial number and MAC address, a site's geographic coordinates.

device_record = ("sw-core-01", "10.1.1.1", "FCW2045L03J")
name, ip, serial = device_record  # unpack into variables
print(name)
# sw-core-01

Tuples use parentheses. Unpacking assigns all values in one line.

Sets — Unique Values Only

A set stores only unique values. Duplicate entries are automatically dropped. Use sets when you need to find unique VLANs, unique sites, or unique device types across a large inventory.

vlans = {10, 20, 10, 30, 20, 10}
print(vlans)
# {10, 20, 30}

Sets are unordered — use sorted() if you need a consistent output order:

print(sorted(vlans))
# [10, 20, 30]

Dictionaries — Device Records

A dictionary maps keys to values. This is how you represent a full device record — hostname maps to IP, IP maps to status, attribute maps to value.

device = {
    "name":        "sw-core-01",
    "ip":          "10.1.1.1",
    "device_type": "switch",
    "site":        "HQ",
    "vlan":        10,
}

print(device["name"])   # sw-core-01
print(device["vlan"])   # 10

Think of a dictionary like a network device's config — each attribute has a key you can look up by name.

Looping Techniques

Loop through a dictionary with .items():

for key, value in device.items():
    print(f"{key}: {value}")

Loop with an index using enumerate():

for i, name in enumerate(["sw-core-01", "sw-access-01"], start=1):
    print(f"{i}. {name}")

Output:

1. sw-core-01
2. sw-access-01

Loop through two lists together with zip():

hostnames = ["sw-core-01", "sw-access-01"]
ips       = ["10.1.1.1",   "10.1.1.2"]

for name, ip in zip(hostnames, ips):
    print(f"{name} — {ip}")

Summary

Lists: ordered, mutable — use for device inventories you need to modify
List comprehensions: filter or transform a list in one line
Tuples: ordered, immutable — use for fixed records like serial numbers
Sets: unordered, unique — use to find unique VLANs or sites
Dictionaries: key-value pairs — use to model full device records
.items(), enumerate(), zip() — tools for looping with more context

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