tuple and set: a Fixed Record and a Collection Without Duplicates

What will we learn?#

Two more data structures, each with a “superpower” of its own:

• tuple — like a list, but fixed: it cannot be changed after it is created.
• set — a collection without duplicates and without order, which lets you check very quickly whether a value is in it.

Why do we need this?#

• A tuple suits data that represents one record with a fixed structure: a point (x, y), a date (2026, 10, 6), a row from a Database (7, "Dana", 24). In the backend and databases topics, every row that comes back from the Database will arrive as a tuple! Being fixed guarantees that no code changes a record “by mistake”.
• A set suits cases where you want uniqueness: how many different users visited the site today? Which tags does a post have? Who is registered for two courses at once?

Explanation from the basics#

tuple#

A tuple is an ordered sequence of values, that cannot be changed (Immutable). Once it is created, you cannot add, remove or replace items.

• Written with round brackets: (1, 2, 3).
• Accessing items is like in a list: point[0], point[-1], len(point), in.
• There is no append, no remove, and no assigning to an item.

Unpacking: you can “unpack” a tuple straight into variables:

student = ("Dana", 24, "Haifa")
name, age, city = student

We already used this without noticing: for name, age in attempts: and for position, name in enumerate(...).

set#

A set is a collection of unique values:

• No duplicates — adding a value that already exists does nothing.
• No order — there are no indexes. my_set[0] is an error. The order when printing can be any order.
• Mutable — you can add and remove.
• A very fast in check, even with a million items. In a list, in goes item by item.
• Written with curly brackets: {1, 2, 3}. But an empty set is created with set(), because {} is an empty dict (the next lesson).

Set operations#

Syntax#

# tuple
point = (3, 5)
single = (7,)              # a tuple with ONE item needs a comma!
x, y = point               # unpacking
point[0]                   # 3

# set
tags = {"python", "web"}
empty_set = set()          # NOT {} - that is an empty dict
tags.add("api")            # add one item
tags.remove("web")         # remove (KeyError if missing)
tags.discard("xyz")        # remove if present, no error if missing
"python" in tags           # fast membership test
unique = set([1, 1, 2])    # {1, 2} - remove duplicates from a list

a | b    # union
a & b    # intersection
a - b    # difference

First code example#

week-2/tuples_demo.py:

student = ("Dana", 24, "Haifa")

print("Full record:", student)
print("Name:", student[0])
print("Fields:", len(student))

name, age, city = student
print(name, "is", age, "and lives in", city)

student[1] = 25

Output:

Full record: ('Dana', 24, 'Haifa')
Name: Dana
Fields: 3
Dana is 24 and lives in Haifa
Traceback (most recent call last):
  File "tuples_demo.py", line 10, in <module>
    student[1] = 25
TypeError: 'tuple' object does not support item assignment

Breaking down the code line by line#

Want to “change” a tuple? Create a new one: student = (student[0], 25, student[2]).

Another example#

Analyzing website users with a set. week-2/visitors.py:

monday_visits = ["dana", "avi", "dana", "noa", "avi", "dana"]
tuesday_visits = ["noa", "yossi", "rina", "noa"]

monday = set(monday_visits)
tuesday = set(tuesday_visits)

print("Monday page views:", len(monday_visits))
print("Monday unique visitors:", len(monday), monday)

print("Visited on both days:", monday & tuesday)
print("Visited on any day:", monday | tuesday)
print("Only on Monday:", monday - tuesday)

tuesday.add("dana")
tuesday.add("noa")
print("Tuesday after adds:", len(tuesday), "unique")
print("Did yossi visit on Monday?", "yossi" in monday)

Output (the order of the items inside {} may be different for you):

Monday page views: 6
Monday unique visitors: 3 {'avi', 'noa', 'dana'}
Visited on both days: {'noa'}
Visited on any day: {'dana', 'yossi', 'rina', 'avi', 'noa'}
Only on Monday: {'avi', 'dana'}
Tuesday after adds: 4 unique
Did yossi visit on Monday? False

Breakdown:

• set(monday_visits) — converts a list to a set, and the duplicates disappear: 6 views, 3 visitors.
• monday & tuesday — intersection: only whoever appears in both (noa).
• monday | tuesday — union: everyone who visited, each one once.
• monday - tuesday — difference: visited on Monday and not on Tuesday.
• tuesday.add("noa") — noa already exists, so nothing happens. Only dana was added, and there are 4 (noa, yossi, rina, dana).

When to use which? A comparison table#

Common mistake#

Mistake 1: a tuple of one item without a comma.

colors = ("red")
print(type(colors))

<class 'str'>

Brackets alone are just arithmetic brackets, like (2 + 3). To create a tuple of one item: ("red",). The comma creates the tuple, not the brackets.

Mistake 2: {} as an empty set.

seen = {}
seen.add("dana")

AttributeError: 'dict' object has no attribute 'add'

{} is an empty dict. An empty set = set().

Mistake 3: expecting order or an index in a set.

names = {"dana", "avi"}
print(names[0])

TypeError: 'set' object is not subscriptable

A set has no “first”. If you need order, convert it to a sorted list: sorted(names).

Mistake 4: Unpacking with a number of variables that does not match.

name, age = ("Dana", 24, "Haifa")

ValueError: too many values to unpack (expected 2)

Practice#

The exercises use only what was taught in this lesson and the lessons before it. Try on your own first, and only then open the solution.

Exercise 1: Unpacking#

student = ("Dana", 24, "Haifa")

Unpack the tuple into three variables in one line, and print a sentence about them. Then try to change the age to 25 — what happens?

Expected output:

Dana is 24 and lives in Haifa

student = ("Dana", 24, "Haifa")

name, age, city = student
print(name, "is", age, "and lives in", city)

Dana is 24 and lives in Haifa

Exercise 2: A function that returns two values#

Write a function min_max(numbers) that returns a tuple of the smallest and the largest. Unpack the result into two variables.

lowest, highest = min_max([40, 3, 99, 17])
print(lowest, highest)

Expected output:

3 99

def min_max(numbers):
    return (min(numbers), max(numbers))


lowest, highest = min_max([40, 3, 99, 17])
print(lowest, highest)

3 99

Exercise 3: Unique visitors#

visits = ["dana", "avi", "dana", "noa", "avi", "dana"]

Print how many views there were, how many different visitors there were, and whether "tom" visited.

Expected output:

6 views
3 visitors
False

visits = ["dana", "avi", "dana", "noa", "avi", "dana"]

unique = set(visits)
print(len(visits), "views")
print(len(unique), "visitors")
print("tom" in unique)

6 views
3 visitors
False

Exercise 4: Set operations#

football = {"dana", "avi", "noa", "tom"}
chess = {"noa", "rina", "tom", "yossi"}

1. Who is in both clubs?
2. Who is only in football?
3. How many different children are there in total?

Print answers 1 and 2 sorted, so that the order is fixed.

Expected output:

['noa', 'tom']
['avi', 'dana']
6

football = {"dana", "avi", "noa", "tom"}
chess = {"noa", "rina", "tom", "yossi"}

print(sorted(football & chess))
print(sorted(football - chess))
print(len(football | chess))

['noa', 'tom']
['avi', 'dana']
6

Exercise 5: list, tuple or set?#

For each case — which structure would you use? Explain.

1. The coordinates of a point on a map: latitude and longitude.
2. A list of tasks that you add to and remove from, in order.
3. The email addresses of everyone who registered — without duplicates.
4. The checkout queue in a supermarket.

Summary#

• tuple ( , ) — ordered, cannot be changed. Suits a record with a fixed structure. One item: (x,).
• Unpacking: a, b = (1, 2). That is how you return and receive several values from a function.
• set { } — no duplicates, no order, no index. An empty set = set().
• set(list) removes duplicates. in on a set is very fast.
• Set operations: | union, & intersection, - difference.
• In the backend and databases topics, rows from the Database will come back as a tuple.

Official documentation#

• Python Tutorial — Tuples and Sequences
• Python Tutorial — Sets
• Built-in Types — Set Types