Coding with Tawfiq | Python Data Structures

DICTIONARIES IN PYTHON

🗂️ Python Dictionary

A dictionary in Python is an ordered collection (from Python 3.7 onwards) of items stored as key/value pairs. Each key is a unique identifier associated with a value.

For example, if we want to store countries and their capitals, we can create a dictionary where the country names are keys and capitals are values.

Creating a Dictionary


capital_city = {"Nepal": "Kathmandu", "Italy": "Rome", "England": "London"}

print(capital_city)

Here:

Keys: "Nepal", "Italy", "England"

Values: "Kathmandu", "Rome", "London"

Keys and values can be of different types.

Example 1: Dictionary with Integer Keys


numbers = {1: "One", 2: "Two", 3: "Three"}

print(numbers)

Adding Elements


capital_city["Japan"] = "Tokyo"

print(capital_city)

Changing Values


student_id = {112: "Kyle", 113: "Maria"}

student_id[112] = "Stan"

print(student_id)

Accessing Elements


print(capital_city["Italy"])  # Output: Rome

# Accessing a non-existing key will raise an error
# print(capital_city["Germany"])  # KeyError

Removing Elements


student_id = {111: "Alice", 112: "Bob"}

del student_id[111]  # removes the key 111

print(student_id)

# del student_id  # deletes the entire dictionary

Dictionary Methods

Dictionaries come with many useful methods such as keys(), values(), items(), get(), and update().

Membership Test


squares = {1: 1, 2: 4, 3: 9}

print(2 in squares)  # True

print(5 in squares)  # False

Iterating Through a Dictionary


squares = {1: 1, 2: 4, 3: 9}

for key in squares:

    print(f"Key: {key}, Value: {squares[key]}")

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💡 Note: You can create dictionaries with mixed key and value types. For example:


random_dict = {"name": "Alice", 1: [10, 20, 30], "is_student": True}

print(random_dict)

📋 Python Lists

Lists are used to store multiple items in a single variable. For example, if we want to record the ages of 5 students, we can create a list instead of separate variables.

Creating a List


numbers = [10, 20, 30]

print(numbers)

A list can contain items of different types, such as integers, floats, and strings:


mixed_list = [10, "Python", 5.5, True]

print(mixed_list)

Accessing List Elements

Each item has an index starting from 0:


languages = ["Python", "Dart", "JavaScript"]

print(languages[0])  # Python

print(languages[-1]) # JavaScript

Slicing Lists


my_list = [10, 20, 30, 40, 50]

print(my_list[2:5])  # [30, 40, 50]

print(my_list[3:])   # [40, 50]

print(my_list[:])    # [10, 20, 30, 40, 50]

Adding Elements

Using append() to add a single item:


numbers.append(40)

print(numbers)  # [10, 20, 30, 40]

Using extend() to merge another list:


even_numbers = [2, 4, 6]

numbers.extend(even_numbers)

print(numbers)  # [10, 20, 30, 40, 2, 4, 6]

Changing List Items


numbers[0] = 100

print(numbers)  # [100, 20, 30, 40, 2, 4, 6]

Removing Elements

Using del:


del numbers[2]

print(numbers)

Using remove():


numbers.remove(4)

print(numbers)

Iterating Through a List


for item in numbers:

    print(item)

List Comprehension

Creates lists in a concise way:


squares = [x**2 for x in range(1,6)]

print(squares)  # [1, 4, 9, 16, 25]

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🔒 Python Tuples

Tuples are similar to lists but are immutable. Once created, elements cannot be changed.

Creating a Tuple


my_tuple = (10, 20, "Python")

print(my_tuple)

Tuple with One Element


var1 = ("hello",)

print(type(var1))  # <class 'tuple'>

var2 = ("hello")

print(type(var2))  # <class 'str'>

Accessing Tuple Elements

Using indexing:


letters = ('a','b','c','d','e','f')

print(letters[0])   # 'a'

print(letters[-1])  # 'f'

print(letters[-3])  # 'd'

Tuple Methods

Only a few methods are available:


my_tuple = ('apple', 'banana', 'apple')

print(my_tuple.count('apple'))  # 2

print(my_tuple.index('banana')) # 1

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🟢 Python Sets

A set is a collection of unique data. Elements of a set cannot be duplicated. For example, we can store student IDs in a set since they are unique.

Creating a Set

We create sets using curly braces {} or the set() function:


numbers = {1, 2, 3, 4}

mixed_set = {1, "Python", 3.5, (2,3)}

print(numbers)

print(mixed_set)

Empty Set


empty_set = set()

empty_dict = {}

print(type(empty_set))      # <class 'set'>

print(type(empty_dict))     # <class 'dict'>

Duplicate Items


numbers = {1, 2, 2, 3, 3, 4}

print(numbers)  # {1, 2, 3, 4} duplicates removed

Adding Items


numbers.add(5)

print(numbers)

Updating a Set


tech_companies = {"Google", "Apple"}

companies = {"Microsoft"}

companies.update(tech_companies)

print(companies)  # {'Microsoft', 'Google', 'Apple'}

Removing Elements


languages = {"Python", "Java", "C++"}

languages.discard("Java")

print(languages)

Set Built-in Functions


numbers = {1, 2, 3, 4}

print(len(numbers))  # 4

print(max(numbers))  # 4

print(min(numbers))  # 1

Set Operations

Union, Intersection, Difference, Symmetric Difference:


A = {1, 2, 3}

B = {2, 3, 4}

print(A | B)              # Union {1, 2, 3, 4}

print(A & B)              # Intersection {2, 3}

print(A - B)              # Difference {1}

print(A ^ B)              # Symmetric Difference {1, 4}

Check Equality


A = {1, 2, 3}

B = {3, 2, 1}

if A == B:

    print("Set A and Set B are equal")

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🔤 Python Strings

In computer programming, a string is a sequence of characters. For example, "hello" contains 'h', 'e', 'l', 'l', 'o'. Strings can be enclosed in single or double quotes in Python.

Creating Strings


string1 = "Python Programming"

name = "Python"

message = "I love Python"

print(string1)

print(name)

print(message)

Accessing String Characters

Three ways to access string characters:


# Indexing

str1 = "Python"

print(str1[0])   # 'P'

print(str1[-1])  # 'n'

# Slicing

print(str1[1:4]) # 'yth'

Immutability


str1 = "Hello"

# str1[0] = 'J'  <-- This will give an error

str1 = "Jello"  # Reassigning variable is allowed

Multiline Strings


multiline = """This is a

multiline string

in Python"""

print(multiline)

String Operations


# Compare Strings

str1 = "Python"

str2 = "Python"

print(str1 == str2)  # True

# Concatenate Strings

greet = "Hello, "

name = "Tawfiq"

print(greet + name)  # "Hello, Tawfiq"

Iterate Through a String


for ch in "Python":

    print(ch)

String Length & Membership


str1 = "Python"

print(len(str1))       # 6

print("P" in str1)     # True

Escape Sequences


text = "He said, \"Python is awesome\""

text2 = 'It\'s Python'

Python f-Strings


name = "Tawfiq"

country = "Tanzania"

print(f'{name} is from {country}')  # Tawfiq is from Tanzania

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💻 Python Practice Tasks

Create a list of integers from user input and compute the sum.
Create a tuple of your 5 favorite books and print each book on a new line.
Create a dictionary to store a person's name, age, and favorite color from user input and print it.
Create two sets of integers from user input and find the common elements.
Store a list of words and use list comprehension to keep only words with an odd number of characters.

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Python Data Structures — learn by examples

DATA STRUCTURE IN PYTHON

DICTIONARIES IN PYTHON