Lists, sets, and dictionaries

Collections hold multiple values, and knowing which one to reach for is a real skill. There are four, but three do almost all the work in security scripting: the list (your targets), the set (your deduper), and the dictionary (every request’s headers, params, and JSON). Get these and you can write real tools.

The four types at a glance

Type	Looks like	Ordered?	Duplicates?	Use it for
list	[1, 2, 3]	yes	yes	an ordered, changeable sequence
tuple	(1, 2, 3)	yes	yes	a fixed sequence that won’t change
set	{1, 2, 3}	no	no	unique items; dedup; fast membership
dict	{"k": "v"}	yes	keys unique	labelled key → value data

Lists — the default sequence

subdomains = ["www", "api", "admin"]
subdomains.append("dev")           # add to the end
subdomains[0]                      # 'www'  (first item, index 0)
subdomains[-1]                     # 'dev'  (last item)
len(subdomains)                    # 4
for sub in subdomains:             # loop over every item
    print(sub)

A list is your default “bunch of things in order” — a list of targets, ports, or payloads to work through.

Sets — your dedup tool

found = ["a.com", "b.com", "a.com"]
unique = set(found)                # {'a.com', 'b.com'} — duplicates gone
"a.com" in unique                  # True — membership check is very fast

Wrap any list in set() and duplicates vanish. This is the recon workhorse: subdomain tools and URL harvesters produce tons of overlap, and a set cleans it instantly.

Dictionaries — labelled data

headers = {
    "User-Agent": "recon/1.0",
    "Authorization": "Bearer abc123",
}
headers["User-Agent"]              # look up by key → 'recon/1.0'
headers["Accept"] = "application/json"   # add or replace a key
for key, value in headers.items(): # loop over pairs
    print(key, "=", value)

The dictionary is the workhorse of HTTP and JSON work. Request headers, query parameters, JSON bodies, and parsed API responses are all dictionaries — labelled key: value data you look up by name. When you learn requests in the next module, you’ll pass dictionaries for headers and params constantly.

Summary

Four containers, three you’ll use constantly. Lists [ ] are ordered, changeable sequences (your targets). Sets { } hold unique items and dedupe instantly (wrap a list in set()). Dictionaries {key: value} hold labelled data and are the shape of HTTP headers, params, JSON bodies, and API responses. Use .get() for keys that might be missing. Tuples are fixed lists you’ll meet occasionally.

Key takeaways

• List = ordered sequence; set = unique items + fast membership; dict = labelled data.
• set(my_list) is the instant deduper.
• Dicts are how you build headers, params, and JSON — learn them well.
• dict.get(key) avoids the KeyError crash on missing keys.

Next, conditions — how your script chooses what to do based on those True/False values.