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<< Day 4 | Day 6 >>

📘 Day 5: Data Structures in Python

Welcome to Day 5 of the 30 Days of Data Science series! Today, we will explore data structures in Python, focusing on three important types:

  • Lists
  • Tuples
  • Dictionaries

Understanding these data structures is fundamental for data manipulation and organization in Python.

Table of Contents

1️⃣ Lists in Python 📋

What is a List?

A list is a mutable (modifiable) collection of ordered elements. Lists can store elements of different data types, such as integers, strings, floats, or even other lists.

Creating a List

# Creating a list of numbers
numbers = [1, 2, 3, 4, 5]

# Creating a mixed data type list
mixed_list = [1, "apple", 3.14, True]

Accessing List Elements

You can access elements in a list using indexing (zero-based).

fruits = ["apple", "banana", "cherry"]

# Accessing the first element
print(fruits[0])  # Output: apple

# Accessing the last element
print(fruits[-1])  # Output: cherry

Adding Elements to a List

Use the append() method to add an element to the end or the insert() method to add at a specific position.

fruits = ["apple", "banana"]

# Adding an element at the end
fruits.append("cherry")
print(fruits)  # Output: ['apple', 'banana', 'cherry']

# Inserting an element at a specific position
fruits.insert(1, "orange")
print(fruits)  # Output: ['apple', 'orange', 'banana', 'cherry']

Removing Elements from a List

Use remove() or pop() to delete elements.

fruits = ["apple", "banana", "cherry"]

# Removing by value
fruits.remove("banana")
print(fruits)  # Output: ['apple', 'cherry']

# Removing by index
fruits.pop(1)
print(fruits)  # Output: ['apple']

List Slicing

Slicing allows you to access a subset of elements.

numbers = [1, 2, 3, 4, 5]

# Getting the first three elements
print(numbers[:3])  # Output: [1, 2, 3]

# Getting elements from index 2 to the end
print(numbers[2:])  # Output: [3, 4, 5]

Common List Methods

Here are some commonly used list methods:

numbers = [1, 2, 3]

# Adding an element
numbers.append(4)

# Counting occurrences
print(numbers.count(2))  # Output: 1

# Sorting the list
numbers.sort()
print(numbers)  # Output: [1, 2, 3, 4]

2️⃣ Tuples in Python 🔗

What is a Tuple?

A tuple is an immutable (unchangeable) collection of ordered elements. Tuples are often used to group related data.

Creating a Tuple

# Creating a tuple of strings
fruits = ("apple", "banana", "cherry")

Accessing Tuple Elements

Similar to lists, you can access tuple elements using indexing.

fruits = ("apple", "banana", "cherry")

print(fruits[0])  # Output: apple

Immutability of Tuples

Tuples cannot be changed after creation. Attempting to modify a tuple results in an error.

fruits = ("apple", "banana", "cherry")

# This will raise an error
fruits[1] = "orange"

Common Tuple Methods

fruits = ("apple", "banana", "cherry")

# Getting the index of an element
print(fruits.index("banana"))  # Output: 1

# Counting occurrences
print(fruits.count("cherry"))  # Output: 1

3️⃣ Dictionaries in Python 📖

What is a Dictionary?

A dictionary is a mutable collection of key-value pairs. Keys must be unique and immutable, while values can be of any type.

Creating a Dictionary

# Creating a dictionary
person = {
    "name": "Alice",
    "age": 25,
    "city": "New York"
}

Accessing Dictionary Values

You can access values using keys.

person = {"name": "Alice", "age": 25}

print(person["name"])  # Output: Alice

Adding and Updating Key-Value Pairs

person = {"name": "Alice", "age": 25}

# Adding a new key-value pair
person["city"] = "New York"

# Updating an existing key
person["age"] = 26

Removing Key-Value Pairs

Use the del keyword or pop() method.

person = {"name": "Alice", "age": 25}

# Removing a key-value pair
del person["age"]

# Using pop()
person.pop("name")

Common Dictionary Methods

person = {"name": "Alice", "age": 25}

# Getting all keys
print(person.keys())  # Output: dict_keys(['name', 'age'])

# Getting all values
print(person.values())  # Output: dict_values(['Alice', 25])

🧠 Practice Exercises

  1. Create a list of your favorite movies and print the last one using negative indexing.
  2. Create a tuple of three numbers and calculate their sum.
  3. Create a dictionary to store information about a book (title, author, year), and add the publisher's name.

🌟 Summary

  • Lists are mutable and ordered collections.
  • Tuples are immutable and ordered collections.
  • Dictionaries store data as key-value pairs and are mutable.