Unit 4 - Lists And Sequences

Lists

Ordered, mutable (changeable) collections of items

Tuples

Ordered, immutable (unchangeable) collections of items

Why Use Lists?

Versatile for storing and manipulating data that might change, like user inpts, evolving datasets, or temporary storage

Why Use Tuples?

Useful for representing fixed collections of data (like coordinates), returning multiple values from functions, or ensuring data integrity where changes are not desired

Differences In Mutability (Lists & Tuples)

Lists can be modified after creation; tuples cannot

Syntax Difference (Lists & Tuples)

Lists use square brackets

Creating Lists

Empty list: my_list = []

With elements: my_list = [1, “hell0”, 3.14]

Creating Tuples

Empty tuple: my_tuple = ()

With elements: my_tuple = (1, “hello”, 3.14)

Accessing Elements (Indexing)

Uses square brackets [] with an index

0-based Indexing

The first element is at index 0

Slicing (Extracting Sub-sequence) Syntax

sequence[start:end:step]

Slicing Start

Inclusive index (defaults to 0)

Slicing End

Exclusive index (defaults to the end of the sequence)

Slicing Step

The increment (defaults to 1)

len(my_list) or len(my_tuple)

Returns the number of elements

Concatenation (Joining)

Uses the + operator

Important About Concatenation

Creates a new list/tuple - does not modify the originals

Repetition

Uses the * operator (with an integer)

Important About Repetition

Creates a new list/tuple

Repetition Code

repeated_list = my_list * 3

my_list.append(item)

Adds item to the end of the list - modifies the list in-place

my_list.extend(another_list)

Appends all elements from another_list to the end of my_list - modifies my_list in-place

Constrast Between Extending And “+”

+ creates a new list; extend modifies the existing one

my_list.insert(index, item)

Inserts item at the specified index - modifies the list in_place

my_list.pop()

Removes and returns the last element - modifies the list in-place

my_list.pop(index)

Removes and returns the element at the specified index - modifies the list in-place

my_list.remove(value)

Removes the first occurrence of value - modifies the list in-place

Caution Of Removing By Value

Raises a ValueError if the value is not found

del my_list[index]

Removes the element at index - modifies the list in-place

del my_list[start:end]

Removes a slice

my_list[index] = new_value

Changes the element at index

my_list[start:end] = another_list

Replaces a slice with elements from another list (sizes don’t have to match)

for item in sequence: Loop

Iterates directly over elements - simple and readable