02-3 The Basics of Python Programming, List Data Type

Hello, in this course, we will take a deep dive into Python’s list data type. Python lists are a very powerful tool for storing and manipulating data. In this article, we will cover everything from the basic usage of lists to advanced features.

What is a List?

A Python list is an ordered collection that can hold items of different data types, and it is a mutable array. The characteristics of Python lists are as follows:

The size of a list can be changed flexibly.
Lists can store various data types.
Each element of the list can be accessed through its index.

Creating and Initializing a List

Creating a list is very simple. You can use square brackets ([]) to enclose items separated by commas.


# Create an empty list
empty_list = []

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

# Create a list of strings
strings = ["apple", "banana", "cherry"]

# Create a list containing various data types
mixed_list = [1, "hello", 3.14, True]

List Indexing and Slicing

Each element of a list can be accessed using an index that starts from 0. Additionally, through the slicing feature, you can easily obtain subsets of a list.


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

# Indexing
print(fruits[0])  # apple
print(fruits[2])  # cherry

# Slicing
print(fruits[1:3])  # ['banana', 'cherry']
print(fruits[:2])   # ['apple', 'banana']
print(fruits[3:])   # ['date', 'fig']

# Negative indexing
print(fruits[-1])  # fig
print(fruits[-3:]) # ['cherry', 'date', 'fig']

List Concatenation and Repetition

Lists can be concatenated using the + operator and repeated using the * operator.


# List concatenation
list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined_list = list1 + list2
print(combined_list)  # [1, 2, 3, 4, 5, 6]

# List repetition
repeated_list = list1 * 3
print(repeated_list)  # [1, 2, 3, 1, 2, 3, 1, 2, 3]

Modifying Lists

To change a specific element of a list, you assign a value using the index. Also, you can add or remove elements from a list.


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

# Modify an element
numbers[2] = 99
print(numbers)  # [1, 2, 99, 4, 5]

# Add an element
numbers.append(6)
print(numbers)  # [1, 2, 99, 4, 5, 6]

# Extend the list
numbers.extend([7, 8, 9])
print(numbers)  # [1, 2, 99, 4, 5, 6, 7, 8, 9]

# Insert an element
numbers.insert(0, 0)
print(numbers)  # [0, 1, 2, 99, 4, 5, 6, 7, 8, 9]

# Remove an element
del numbers[2]
print(numbers)  # [0, 1, 99, 4, 5, 6, 7, 8, 9]

numbers.remove(99)
print(numbers)  # [0, 1, 4, 5, 6, 7, 8, 9]

# Clear the list
numbers.clear()
print(numbers)  # []

List Methods

Python lists offer a variety of useful methods. You can use these methods to extend the functionality of lists.


numbers = [3, 6, 1, 7, 2, 8, 10, 4]

# Length of the list
length = len(numbers)
print(length)  # 8

# Maximum/Minimum value in the list
max_value = max(numbers)
min_value = min(numbers)
print(max_value)  # 10
print(min_value)  # 1

# Finding the index of an element
index_of_seven = numbers.index(7)
print(index_of_seven)  # 3

# Counting occurrences of an element
count_of_ten = numbers.count(10)
print(count_of_ten)  # 1

# Sorting the list
numbers.sort()
print(numbers)  # [1, 2, 3, 4, 6, 7, 8, 10]

# Sorting the list in reverse order
numbers.sort(reverse=True)
print(numbers)  # [10, 8, 7, 6, 4, 3, 2, 1]

# Reversing the list
numbers.reverse()
print(numbers)  # [1, 2, 3, 4, 6, 7, 8, 10]

# Copying the list
numbers_copy = numbers.copy()
print(numbers_copy)  # [1, 2, 3, 4, 6, 7, 8, 10]

Advanced Uses of Lists

Lists provide a variety of advanced functionalities that can be used effectively. Next, we will learn about list comprehensions, nested lists, and various transformation operations.

List Comprehensions

List comprehensions are a concise way to create new lists based on existing lists. They enhance code readability and often improve execution speed.


# Creating a list in a typical way
squares = []
for x in range(10):
    squares.append(x**2)

print(squares)  # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# List comprehension
squares = [x**2 for x in range(10)]
print(squares)  # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# List comprehension with a condition
even_squares = [x**2 for x in range(10) if x % 2 == 0]
print(even_squares)  # [0, 4, 16, 36, 64]

Nested Lists

Lists can contain other lists as elements, allowing you to create multi-dimensional data structures. Nested lists are particularly useful for handling multi-dimensional data like matrices.


# Example of a nested list: 2x3 matrix
matrix = [
    [1, 2, 3],
    [4, 5, 6]
]

# Accessing elements of a nested list
first_row = matrix[0]
print(first_row)  # [1, 2, 3]

element = matrix[1][2]
print(element)  # 6

# Transposing a matrix
transpose = [[row[i] for row in matrix] for i in range(3)]
print(transpose)  # [[1, 4], [2, 5], [3, 6]]

List Transformations

Lists can be easily transformed into other data structures, allowing you to alter the form of the data or create new structures with specific characteristics.


# Converting a list to a string
words = ['Python', 'is', 'awesome']
sentence = ' '.join(words)
print(sentence)  # "Python is awesome"

# Converting a string to a list
letters = list("Python")
print(letters)  # ['P', 'y', 't', 'h', 'o', 'n']

# Converting lists and tuples
tuple_from_list = tuple(numbers)
print(tuple_from_list)  # (1, 2, 3, 4, 6, 7, 8, 10)

list_from_tuple = list((1, 2, 3))
print(list_from_tuple)  # [1, 2, 3]

Conclusion

In this lesson, we explored Python’s list data type. Lists are one of the most widely used data structures in Python, offering a powerful tool for flexibly handling various data. By understanding both basic and advanced usage, I hope you upgrade your Python programming skills. In future lessons, we will cover even more diverse topics and applications, so I hope you look forward to it!

02-3 Basics of Python Programming, List Data Type