Data Structures: Lists, Dicts & Sets

Work with Python's core built-in containers: lists, tuples, dictionaries, and sets — and apply them to real security use cases.

Easy 55m 3 tasks

Prerequisites: Control Flow & Functions

Learning Objectives

→ Create and manipulate lists, tuples, dicts, and sets
→ Use list comprehensions for concise data transformation
→ Apply dicts to store structured data like scan results
→ Use sets for deduplication and membership testing
→ Understand mutability and when to use each structure

Lists

An ordered, mutable sequence:

open_ports = [22, 80, 443, 8080]
open_ports.append(3306)
open_ports.insert(0, 21)
open_ports.remove(8080)
print(open_ports[0])      # first item
print(open_ports[-1])     # last item
print(open_ports[1:3])    # slice [80, 443]
print(len(open_ports))    # count

Useful methods: append, extend, insert, remove, pop, sort, reverse, index, count.

List Comprehensions

ports    = range(1, 1025)
high     = [p for p in ports if p > 1000]
squared  = [p**2 for p in [1,2,3,4]]
services = [f"port_{p}" for p in [22, 80, 443]]

Tuples

Immutable sequences — use for fixed data:

endpoint = ("192.168.1.1", 443)
host, port = endpoint           # unpacking
print(endpoint[1])              # 443

Tuples are hashable, so they can be dict keys or set members.

Dictionaries

Key-value store — O(1) lookup:

scan_result = {
    "host":     "192.168.1.1",
    "ports":    [22, 80, 443],
    "os":       "Linux",
    "is_up":    True,
}

print(scan_result["host"])
scan_result["mac"] = "AA:BB:CC:DD:EE:FF"    # add key
del scan_result["is_up"]                     # remove key
print(scan_result.get("version", "unknown")) # safe get

Iterating:

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

keys   = list(scan_result.keys())
values = list(scan_result.values())

Nested dicts for multi-host results:

network = {
    "192.168.1.1": {"ports": [22, 80], "os": "Linux"},
    "192.168.1.2": {"ports": [3389],   "os": "Windows"},
}
for ip, info in network.items():
    print(ip, "→", info["ports"])

Sets

Unordered, unique elements:

seen_ips = {"10.0.0.1", "10.0.0.2", "10.0.0.1"}
print(seen_ips)        # {'10.0.0.1', '10.0.0.2'} — deduped

seen_ips.add("10.0.0.3")
seen_ips.discard("10.0.0.2")    # no error if missing
print("10.0.0.1" in seen_ips)   # True — O(1) lookup

Set operations (great for comparing scan results):

baseline = {"22", "80", "443"}
current  = {"22", "80", "8080"}
new_ports    = current - baseline        # {"8080"}  — difference
closed_ports = baseline - current        # {"443"}
common       = baseline & current        # {"22","80"} — intersection
all_ports    = baseline | current        # union

Choosing the Right Structure

Structure	Ordered	Mutable	Unique	Use case
list	✓	✓	✗	Sequences, port lists
tuple	✓	✗	✗	Fixed records, dict keys
dict	✓ (3.7+)	✓	keys	Lookup tables, scan results
set	✗	✓	✓	Dedup, membership tests

Mini Project – Baseline Diff

import json

baseline  = {"22", "80", "443"}
current   = {"22", "80", "8080", "3306"}

new   = current - baseline
gone  = baseline - current

print("NEW PORTS:",    new   or "none")
print("CLOSED PORTS:", gone  or "none")
result = {"new": list(new), "closed": list(gone)}
print(json.dumps(result, indent=2))