Data Structures · Unit 3

Tuples

Ordered, unchangeable collections

Unit 3 · Data Structures

Choose the right container for your data

A data structure organizes values so a program can find and work with them. Explore four built-in Python structures and use each lab to see how its rules affect real data.

Lists

Ordered and changeable

Tuples

Ordered and fixed

Sets

Unique values

Dictionaries

Key → value lookup

Ordered · not changeable · duplicates allowed

Tuples: a fixed record of values

A tuple stores a sequence like a list, but its items cannot be reassigned, added, or removed after creation. Use parentheses for clarity; a one-item tuple needs a trailing comma, such as (5,).

Think of a printed result slip: its recorded marks stay fixed. You can read a position or copy its values into new names, but the original tuple remains unchanged.

Tuple index explorer

Select a position to retrieve its value. The tuple has four marks and cannot be edited in this lab.

index 091

index 182

index 276

index 388

marks[0] returns 91.

marks[0]Read by position.

marks[:2]Slice the first two values.

a, b = (1, 2)Unpack values into names.

Read and unpack a tuple

Starting up Python…

marks = [91,82,76,88]
print("Selected item:", marks[0])
print("First two:", marks[:2])
first, second, *remaining = marks
print("Unpacked:", first, second, remaining)

The editor is ready while Python loads in the background.

Output

Your program's output will appear here.

Common Python mistakes

NameError: name 'mark' is not defined

NameError: A name was used before Python could find a variable or function with that name.

IndexError: list index out of range

IndexError: The requested position is outside the items in this list or sequence.

KeyError: 'email'

KeyError: That key does not exist in this dictionary.

TypeError: can only concatenate str (not "int") to str

TypeError: This operation does not work with the kind of value it received.

ZeroDivisionError: division by zero

ZeroDivisionError: A number cannot be divided by zero.

SyntaxError: invalid syntax

SyntaxError: Python could not understand the structure of this line. Check spelling, brackets, colons, and quotes.

IndentationError: expected an indented block

IndentationError: The spaces at the start of a line do not match Python's block structure.

Avoid common tuple mistakes

Parentheses alone do not make a one-item tuple: write ("OS",), including the comma.
Tuples are immutable: assigning marks[0] = 100 raises a TypeError. Create a new tuple if the values must change.
Unpacking needs matching values: each target name needs a corresponding value unless extended unpacking is used.

Tuples check

1. How do you write a tuple containing only the number 5?

2. Can you replace an item in an existing tuple?

Compare the four structures

Ask two questions: does order matter, and should the collection change after creation?

Structure	Ordered?	Changeable?	Access values by
list	Yes	Yes	Position (index)
tuple	Yes	No	Position (index)
set	No guaranteed order	Yes	Membership, not index
dict	Insertion order is preserved	Yes	Key

Use a list for a sequence that changes, a tuple for a fixed record, a set for unique membership, and a dictionary for named lookups.

Lists Sets