Data Structures in Python

CONTENTS

1. Built-in Data Structures

2. Input/ Output Function

3. Control Flow

01

Built-in Data Structures

Lists

Lists are ordered, mutable (changeable), and allow duplicate elements.

They are defined using square brackets []. Items are separated by commas (,).

We can access elements by passing the position and can also change values.

Lists

List Methods

Method	Purpose	Example
append(x)	Adds an item to the end of the list	list.append(10)
insert(i, x)	Inserts an item at index i	list.insert(2, 50)
remove(x)	Removes the first occurrence of value x	list.remove(3)
pop(i)	Removes and returns item at index i (default last)	list.pop()
clear()	Removes all items from the list	list.clear()
sort()	Sorts the list in ascending order	list.sort()
reverse()	Reverses the list order	list.reverse()
count(x)	Returns how many times x appears	list.count(5)
index(x)	Returns the index of the first occurrence of x	list.index("apple")
extend(iterable)	Adds multiple items (joins lists)	list.extend([4,5])
len()	Returns the number of elements	len(l)

Tuples

Tuples are ordered, immutable (unchangeable), and allow duplicate elements.

They are defined using parentheses ().

Tuples

Tuple Methods

Method	Purpose	Example
count(x)	Returns how many times value x appears in the tuple	t.count(2)
index(x)	Returns the index of the first occurrence of x	t.index("apple")
len()	Returns the number of elements	len(l)

Example of Tuple

Creating a tuple

my_tuple = (1, 2, 3, 4, 5) print(my_tuple) /# Output: (1, 2, 3, 4, 5)

Accessing elements

print(my_tuple[0]) /# Output: 1 (first element) print(my_tuple[-1]) /# Output: 5 (last element)

Tuples are immutable; you cannot modify elements.

/# my_tuple[1] = 10 /# This will raise a TypeError

Tuples can be used to store heterogeneous data

person = ("Alice", 30, "Engineer") print(person) /# Output: ('Alice', 30, 'Engineer')

Dictionaries

• Dictionaries are ordered, mutable, and use key-value pairs to store data.

• Keys are unique, and values can be of any data type.

• They are defined using curly braces {}.

Dictionary Methods

Method	Purpose	Example
get(key)	Returns the value of the given key (does not show error if key doesn’t exist)	d.get("name")
keys()	Returns all keys in the dictionary	d.keys()
values()	Returns all values in the dictionary	d.values()
items()	Returns all key-value pairs as tuples	d.items()
update(d2)	Updates dictionary with elements from another dictionary	d.update({"age": 21})
pop(key)	Removes the item with the given key	d.pop("name")
popitem()	Removes the last inserted key-value pair	d.popitem()
clear()	Removes all items from the dictionary	d.clear()

Example of Dictionary

Creating a dictionary

my_dict = {"name": "Alice", "age": 30, "city": "New York"} print(my_dict) /# Output: {'name': 'Alice', 'age': 30, 'city': 'New York'}

Accessing values

print(my_dict["name"]) /# Output: Alice

Modifying values

my_dict["age"] = 31 print(my_dict) /# Output: {'name': 'Alice', 'age': 31, 'city': 'New York'}

Adding new key-value pairs

my_dict["occupation"] = "Engineer" print(my_dict) /# Output: {'name': 'Alice', 'age': 31, 'city': 'New York', 'occupation': 'Engineer'}

Removing key-value pairs

del my_dict["city"] print(my_dict) /# Output: {'name': 'Alice', 'age': 31, 'occupation': 'Engineer'}

Sets

A set is a collection of unique elements (no duplicates).

It is unordered, meaning the items do not have a fixed position.

Sets are mutable, so we can add or remove elements.

Sets

Set Methods

Method	Purpose	Example
add(x)	Adds an element	s.add(10)
remove(x)	Removes x (error if not found)	s.remove(3)
discard(x)	Removes x (no error if not found)	s.discard(3)
clear()	Removes all items	s.clear()
union(s2)	Combines sets	s1.union(s2)
intersection(s2)	Common elements	s1.intersection(s2)

Frozenset

Immutable version of a set (cannot be changed after creation).

No add(), remove(), etc.

Supports only reading operations like union() and intersection.

Frozenset

Example:

fs = frozenset({1, 2, 3})

Difference Between List, Tuple, Set, and Dictionary

Feature	List	Tuple	Set	Dictionary
Definition	Ordered collection of items	Ordered collection of items	Unordered collection of unique items	Collection of key–value pairs
Syntax	[]	()	{}	{key: value}
Mutability	Mutable (can change values)	Immutable (cannot change values)	Mutable, but elements must be unique	Mutable (keys are unique)
Allows	Yes	Yes	No	Keys: No, Values: Yes
Indexing	Supported	Supported (fixed data that shouldn’t change)	Not supported	Accessed using key
Best Used	General purpose data storage	Supported (fixed data that shouldn’t change)	Removing duplicates, math set operations	Data mapped as key → value pairs

02

Input/ Output Function

Input/ Output Function

The input() function is used to take input from the user. It reads a line from input, converts it into a string, and returns it.

name = input("Enter your name: ") print(f"Hello, {name}!")

The print() function is used to display output to the console. It can take multiple arguments, which are printed with a space between them by default.

name = "Alice" age = 30 print("Name:", name, "Age:", age)

03

Control Flow

Control Flow

Control flow statements in Python allow you to manage the execution of code based on certain conditions or repeatedly execute code blocks.

Conditional Statements

if Statement

Executes a block of code if a specified condition is true. Example:

age = 18 if age >= 18: print("You are an adult.")

if-else Statement

Executes one block of code if the condition is true, and another block if it is false. Example:

age = 16 if age >= 18: print("You are an adult.") else: print("You are not an adult.")

if-elif-else Statement

Allows you to check multiple conditions. If the first condition is false, it checks the next one, and so on. Example:

age = 20 if age < 13: print("You are a child.") elif age < 20: print("You are a teenager.") else: print("You are an adult.")

Thank You