Back to Python Course

Python Course

Basic Data Structures

Python provides several built-in data structures that help you store and organize collections of data. Each structure has different properties like ordering, mutability, and uniqueness.

Common Data Structures:

Type	Example	                          Description
list	[1, 2, 3]	                      Ordered, mutable
tuple	(1, 2, 3)	                      Ordered, immutable
set	    {1, 2, 3}	                      Unordered, unique items
dict	{"name": "Praveen", "age": 39}	  Key-value pairs

Let's see some examples,

# List - Mutable and ordered
fruits = ["apple", "banana", "cherry"]

# Tuple - Immutable and ordered
coordinates = (10.0, 20.5)

# Set - Unordered, unique elements
unique_numbers = {1, 2, 3, 2}

# Dictionary - Key-value pairs
person = {"name": "Praveen", "age": 39}

Key Characteristics:

  • List (list):

    • Defined with square brackets []
    • Items are ordered and can be changed
    • Allows duplicates

  • Tuple (tuple):

    • Defined with parentheses ()
    • Ordered like a list, but cannot be modified (immutable)

  • Set (set):

    • Defined with curly braces {} (like a dictionary but without key-value pairs)
    • Unordered
    • Does not allow duplicates

  • Dictionary (dict):

    • Stores key-value pairs
    • Defined with curly braces and colons {key: value}
    • Keys must be unique

Accessing Elements:

print(fruits[0])            # List indexing: apple
print(coordinates[1])       # Tuple indexing: 20.5
print("banana" in fruits)   # Membership check: True
print(person["name"])       # Access by key: Praveen

Use the type() function to confirm the data structure:

print(type(fruits))     # <class 'list'>
print(type(coordinates))# <class 'tuple'>
print(type(unique_numbers)) # <class 'set'>
print(type(person))     # <class 'dict'>

Lists

List Slicing

myList=[1,2,3,4,5]
print(myList[3:]) # It prints [4, 5]
print(myList[0:6:2]) # It prints [1, 3, 5]
print(myList[0:6:3]) # It prints [1, 4]
print(myList[::2]) # It prints [1, 3, 5]
print(list(range(10))) # It prints [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Modifying Lists

myList = [1,2,3,4]
myList.append(5)
print(myList) # It prints [1, 2, 3, 4, 5]

myList.insert(3,8)
print(myList) # It prints [1, 2, 3, 8, 4, 5]

myList.remove(8)
print(myList) # It prints [1, 2, 3, 4, 5]

myList.pop()
print(myList) # It prints [1, 2, 3, 4]
print(len(myList))  # It prints 4

a = [1,2,3,4,5]
b = a
a.append(6)
print(b) # It prints [1, 2, 3, 4, 5, 6]
print(a) # It prints [1, 2, 3, 4, 5, 6]

a = [1,2,3,4,5]
b = a.copy()
a.append(6)
print(b) # It prints [1, 2, 3, 4, 5]
print(a) # It prints [1, 2, 3, 4, 5, 6]

Sets

mySet = {'a','b','c','d'}
print(mySet) # It prints {'a', 'b', 'd', 'c'} or in any order, as sets do not maintain order


mySet = set({'a','b','c','d'})
print(mySet) # It prints {'a', 'b', 'd', 'c'}

myList = ['a','b','c','d','c', 'b']
myList = list(set(myList))
print(myList) # It removes duplicates and prints ['a', 'b', 'd', 'c'] or in any order

mySet.add('e') 
print(mySet) # It prints {'c', 'd', 'a', 'e', 'b'} or in any order

print('a' in mySet) # It prints True
print('p' in mySet) # It prints False

print(len(mySet)) # It prints 5

mySet.discard('a')
print(mySet) # It prints {'c', 'd', 'e', 'b'} or in any order

Tuples

A tuple is similar to a list, but it is declared using parentheses () instead of square brackets [].

Tuples are immutable, meaning their elements cannot be changed after creation.

myTuple = ('a','b','c','d')
print(myTuple) # It prints ('a', 'b', 'c', 'd')

Why we use Tuples?

Let's say we are building a delivery tracking app. We need to store the GPS coordinates (latitude, longitude) of delivery locations. Since these coordinates should not be changed once recorded, a tuple is perfect.

# List of delivery locations as (latitude, longitude) tuples
delivery_locations = [
    (37.7749, -122.4194),  # San Francisco
    (34.0522, -118.2437),  # Los Angeles
    (40.7128, -74.0060),   # New York
]

# Display delivery locations
for index, location in enumerate(delivery_locations, start=1):
    print(f"Delivery {index} Location: Latitude = {location[0]}, Longitude = {location[1]}")

Output

Delivery 1 Location: Latitude = 37.7749, Longitude = -122.4194
Delivery 2 Location: Latitude = 34.0522, Longitude = -118.2437
Delivery 3 Location: Latitude = 40.7128, Longitude = -74.0060

Why Use Tuples Here?

  • Coordinates should not change — tuples ensure immutability.
  • Tuples use less memory than lists.
  • We are not performing operations that require mutability.

Dictionaries

A dictionary in Python is a collection of key-value pairs, where each key is unique and maps to a specific value.

Let's see an example, imagine we are building a student management system where we store and retrieve student details.

# Dictionary of student records
student_records = {
    "S101": {"name": "Praveen", "grade": "A", "age": 39},
    "S102": {"name": "Ravi", "grade": "B", "age": 38},
    "S103": {"name": "Praneeth", "grade": "A", "age": 40}
}

# Access a specific student's details
student_id = "S102"
if student_id in student_records:
    print(f"Student Name: {student_records[student_id]['name']}")
    print(f"Grade: {student_records[student_id]['grade']}")
else:
    print("Student not found.")

# Add a new student
student_records["S104"] = {"name": "Divya", "grade": "C", "age": 34}

# Update an existing student's grade
student_records["S103"]["grade"] = "A+"

# Remove a student
student_records.pop("S103")

# Display all student records
print("\nAll Student Records:")
for sid, info in student_records.items():
    print(f"ID: {sid}, Name: {info['name']}, Grade: {info['grade']}, Age: {info['age']}")

Output

Student Name: Ravi
Grade: B

All Student Records:
ID: S101, Name: Praveen, Grade: A, Age: 39
ID: S102, Name: Ravi, Grade: B, Age: 38
ID: S104, Name: Divya, Grade: C, Age: 34