01_lists.py

"""
================================================================================
File: 01_lists.py
Topic: Python Lists - Ordered, Mutable Collections
================================================================================

This file demonstrates Python lists, which are ordered, mutable collections
that can store elements of any type. Lists are one of the most versatile
and commonly used data structures in Python.

Key Concepts:
- Creating and accessing lists
- List methods (append, insert, remove, pop, etc.)
- Slicing and indexing
- List operations (concatenation, repetition)
- Nested lists
- List comprehensions

================================================================================
"""

# -----------------------------------------------------------------------------
# 1. Creating Lists
# -----------------------------------------------------------------------------
# Lists are created with square brackets []

print("--- Creating Lists ---")

# Empty list
empty_list = []
print(f"Empty list: {empty_list}")

# List with elements
numbers = [1, 2, 3, 4, 5]
fruits = ["apple", "banana", "cherry"]
mixed = [1, "hello", 3.14, True, None]

print(f"Numbers: {numbers}")
print(f"Fruits: {fruits}")
print(f"Mixed types: {mixed}")

# Using list() constructor
chars = list("Python")
print(f"From string: {chars}")

# List from range
range_list = list(range(1, 6))
print(f"From range: {range_list}")

# -----------------------------------------------------------------------------
# 2. Accessing Elements (Indexing)
# -----------------------------------------------------------------------------
# Lists are zero-indexed; negative indices count from the end

print("\n--- Indexing ---")

colors = ["red", "green", "blue", "yellow", "purple"]

print(f"List: {colors}")
print(f"First element (index 0): {colors[0]}")
print(f"Third element (index 2): {colors[2]}")
print(f"Last element (index -1): {colors[-1]}")
print(f"Second to last (index -2): {colors[-2]}")

# -----------------------------------------------------------------------------
# 3. Slicing Lists
# -----------------------------------------------------------------------------
# Syntax: list[start:stop:step]

print("\n--- Slicing ---")

nums = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
print(f"Original: {nums}")

print(f"nums[2:5]: {nums[2:5]}")       # Elements 2, 3, 4
print(f"nums[:4]: {nums[:4]}")          # First 4 elements
print(f"nums[6:]: {nums[6:]}")          # From index 6 to end
print(f"nums[::2]: {nums[::2]}")        # Every 2nd element
print(f"nums[::-1]: {nums[::-1]}")      # Reversed list
print(f"nums[1:8:2]: {nums[1:8:2]}")    # Odd indices from 1 to 7

# -----------------------------------------------------------------------------
# 4. Modifying Lists
# -----------------------------------------------------------------------------
# Lists are mutable - you can change their contents

print("\n--- Modifying Lists ---")

languages = ["Python", "Java", "C++"]
print(f"Original: {languages}")

# Change single element
languages[1] = "JavaScript"
print(f"After changing index 1: {languages}")

# Change multiple elements with slicing
languages[0:2] = ["Rust", "Go"]
print(f"After slice replacement: {languages}")

# -----------------------------------------------------------------------------
# 5. List Methods
# -----------------------------------------------------------------------------
# Built-in methods to manipulate lists

print("\n--- List Methods ---")

# append() - Add element to end
items = [1, 2, 3]
items.append(4)
print(f"After append(4): {items}")

# extend() - Add multiple elements
items.extend([5, 6])
print(f"After extend([5, 6]): {items}")

# insert() - Add element at specific position
items.insert(0, 0)  # Insert 0 at index 0
print(f"After insert(0, 0): {items}")

# remove() - Remove first occurrence of value
items.remove(3)
print(f"After remove(3): {items}")

# pop() - Remove and return element at index (default: last)
popped = items.pop()
print(f"Popped: {popped}, List now: {items}")

popped = items.pop(0)
print(f"Popped at 0: {popped}, List now: {items}")

# index() - Find index of first occurrence
fruits = ["apple", "banana", "cherry", "banana"]
print(f"\nfruits = {fruits}")
print(f"Index of 'banana': {fruits.index('banana')}")

# count() - Count occurrences
print(f"Count of 'banana': {fruits.count('banana')}")

# sort() - Sort in place
numbers = [3, 1, 4, 1, 5, 9, 2, 6]
numbers.sort()
print(f"\nAfter sort(): {numbers}")

numbers.sort(reverse=True)
print(f"After sort(reverse=True): {numbers}")

# reverse() - Reverse in place
numbers.reverse()
print(f"After reverse(): {numbers}")

# copy() - Create a shallow copy
original = [1, 2, 3]
copied = original.copy()
print(f"\nOriginal: {original}, Copy: {copied}")

# clear() - Remove all elements
copied.clear()
print(f"After clear(): {copied}")

# -----------------------------------------------------------------------------
# 6. List Operations
# -----------------------------------------------------------------------------

print("\n--- List Operations ---")

# Concatenation (+)
list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined = list1 + list2
print(f"{list1} + {list2} = {combined}")

# Repetition (*)
repeated = [0] * 5
print(f"[0] * 5 = {repeated}")

# Membership (in)
fruits = ["apple", "banana", "cherry"]
print(f"'banana' in fruits: {'banana' in fruits}")
print(f"'grape' in fruits: {'grape' in fruits}")

# Length
print(f"len(fruits): {len(fruits)}")

# Min and Max
numbers = [5, 2, 8, 1, 9]
print(f"min({numbers}): {min(numbers)}")
print(f"max({numbers}): {max(numbers)}")
print(f"sum({numbers}): {sum(numbers)}")

# -----------------------------------------------------------------------------
# 7. Nested Lists (2D Lists)
# -----------------------------------------------------------------------------

print("\n--- Nested Lists ---")

# Creating a 2D list (matrix)
matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

print("Matrix:")
for row in matrix:
    print(f"  {row}")

# Accessing elements
print(f"\nElement at [1][2]: {matrix[1][2]}")  # Row 1, Column 2 = 6
print(f"Second row: {matrix[1]}")

# Modifying nested element
matrix[0][0] = 100
print(f"After matrix[0][0] = 100: {matrix[0]}")

# -----------------------------------------------------------------------------
# 8. List Comprehensions
# -----------------------------------------------------------------------------
# Concise way to create lists

print("\n--- List Comprehensions ---")

# Basic list comprehension
squares = [x**2 for x in range(1, 6)]
print(f"Squares 1-5: {squares}")

# With condition
even_squares = [x**2 for x in range(1, 11) if x % 2 == 0]
print(f"Even squares: {even_squares}")

# With expression
words = ["hello", "world", "python"]
upper_words = [word.upper() for word in words]
print(f"Uppercase: {upper_words}")

# Nested comprehension (flattening)
matrix = [[1, 2], [3, 4], [5, 6]]
flattened = [num for row in matrix for num in row]
print(f"Flattened: {flattened}")

# -----------------------------------------------------------------------------
# 9. Copying Lists - Shallow vs Deep
# -----------------------------------------------------------------------------

print("\n--- Copying Lists ---")

import copy

# Shallow copy - nested objects share reference
original = [[1, 2], [3, 4]]
shallow = original.copy()
shallow[0][0] = 999  # Affects both!
print(f"Shallow copy issue:")
print(f"  Original: {original}")
print(f"  Shallow: {shallow}")

# Deep copy - completely independent
original = [[1, 2], [3, 4]]
deep = copy.deepcopy(original)
deep[0][0] = 999  # Only affects copy
print(f"\nDeep copy:")
print(f"  Original: {original}")
print(f"  Deep: {deep}")

# -----------------------------------------------------------------------------
# 10. Practical Examples
# -----------------------------------------------------------------------------

print("\n--- Practical Examples ---")

# Finding unique elements while preserving order
items = [1, 2, 2, 3, 3, 3, 4, 4, 4, 4]
unique = []
for item in items:
    if item not in unique:
        unique.append(item)
print(f"Unique elements: {unique}")

# Filtering with list comprehension
scores = [85, 42, 91, 78, 55, 99, 66]
passing = [score for score in scores if score >= 60]
print(f"Passing scores: {passing}")

# Transforming data
temperatures_c = [0, 10, 20, 30, 40]
temperatures_f = [(c * 9/5) + 32 for c in temperatures_c]
print(f"Celsius: {temperatures_c}")
print(f"Fahrenheit: {temperatures_f}")