# Empty list
empty = []
empty = list()

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

# Nested lists
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# From other iterables
chars = list("Python")     # ['P', 'y', 't', 'h', 'o', 'n']
nums = list(range(1, 6))   # [1, 2, 3, 4, 5]

# Repeated values
zeros = [0] * 5  # [0, 0, 0, 0, 0]

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

# Indexing (0-based)
print(fruits[0])    # apple
print(fruits[2])    # cherry
print(fruits[-1])   # elderberry (last element)
print(fruits[-2])   # date

# Slicing [start:stop:step]
print(fruits[1:3])    # ['banana', 'cherry']
print(fruits[:3])     # ['apple', 'banana', 'cherry']
print(fruits[2:])     # ['cherry', 'date', 'elderberry']
print(fruits[::2])    # ['apple', 'cherry', 'elderberry']
print(fruits[::-1])   # reversed list

# Nested list access
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
print(matrix[0])      # [1, 2, 3]
print(matrix[1][2])   # 6

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

# Change an element
fruits[1] = "blueberry"
print(fruits)  # ['apple', 'blueberry', 'cherry']

# Change a range
fruits[1:3] = ["grape", "kiwi", "mango"]
print(fruits)  # ['apple', 'grape', 'kiwi', 'mango']

fruits = ["apple", "banana"]

# append() - add to end
fruits.append("cherry")
print(fruits)  # ['apple', 'banana', 'cherry']

# insert() - add at specific position
fruits.insert(1, "blueberry")
print(fruits)  # ['apple', 'blueberry', 'banana', 'cherry']

# extend() - add multiple items
fruits.extend(["date", "elderberry"])
print(fruits)  # ['apple', 'blueberry', 'banana', 'cherry', 'date', 'elderberry']

# Using += operator
fruits += ["fig"]
print(fruits)  # [..., 'fig']

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

# remove() - remove first occurrence by value
fruits.remove("banana")
print(fruits)  # ['apple', 'cherry', 'banana', 'date']

# pop() - remove by index and return it
last = fruits.pop()       # Remove last
print(last)               # date
second = fruits.pop(1)    # Remove index 1
print(second)             # cherry

# del - delete by index or slice
del fruits[0]
print(fruits)  # ['banana']

# clear() - remove all elements
fruits.clear()
print(fruits)  # []

numbers = [3, 1, 4, 1, 5, 9, 2, 6]

# sort() - modifies in place
numbers.sort()
print(numbers)  # [1, 1, 2, 3, 4, 5, 6, 9]

# Reverse sort
numbers.sort(reverse=True)
print(numbers)  # [9, 6, 5, 4, 3, 2, 1, 1]

# sorted() - returns new list (original unchanged)
original = [3, 1, 4, 1, 5]
sorted_list = sorted(original)
print(original)     # [3, 1, 4, 1, 5] (unchanged)
print(sorted_list)  # [1, 1, 3, 4, 5]

# Sort with key function
words = ["banana", "apple", "cherry", "date"]
words.sort(key=len)
print(words)  # ['date', 'apple', 'banana', 'cherry']

# Sort objects
students = [("Alice", 85), ("Bob", 92), ("Charlie", 78)]
students.sort(key=lambda s: s[1], reverse=True)
print(students)  # [('Bob', 92), ('Alice', 85), ('Charlie', 78)]

# Basic: [expression for item in iterable]
squares = [x ** 2 for x in range(10)]
print(squares)  # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# With condition: [expression for item in iterable if condition]
evens = [x for x in range(20) if x % 2 == 0]
print(evens)  # [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

# With if-else
labels = ["even" if x % 2 == 0 else "odd" for x in range(5)]
print(labels)  # ['even', 'odd', 'even', 'odd', 'even']

# Nested comprehension
matrix = [[i * j for j in range(1, 4)] for i in range(1, 4)]
print(matrix)  # [[1, 2, 3], [2, 4, 6], [3, 6, 9]]

# Flatten a nested list
matrix = [[1, 2], [3, 4], [5, 6]]
flat = [num for row in matrix for num in row]
print(flat)  # [1, 2, 3, 4, 5, 6]

# String processing
words = ["Hello", "World", "Python"]
upper = [w.upper() for w in words]
print(upper)  # ['HELLO', 'WORLD', 'PYTHON']

lengths = {w: len(w) for w in words}
print(lengths)  # {'Hello': 5, 'World': 5, 'Python': 6}

# Length
print(len([1, 2, 3]))  # 3

# Membership
print(3 in [1, 2, 3])      # True
print(5 not in [1, 2, 3])  # True

# Concatenation
print([1, 2] + [3, 4])  # [1, 2, 3, 4]

# Repetition
print([0] * 3)  # [0, 0, 0]

# Min, max, sum
nums = [3, 1, 4, 1, 5]
print(min(nums))  # 1
print(max(nums))  # 5
print(sum(nums))  # 14

# any() and all()
print(any([False, False, True]))  # True (at least one True)
print(all([True, True, True]))    # True (all True)
print(all([True, False, True]))   # False

original = [1, [2, 3], 4]

# Shallow copy methods (all equivalent)
copy1 = original.copy()
copy2 = original[:]
copy3 = list(original)

# Shallow copy shares nested objects!
copy1[1][0] = 99
print(original)  # [1, [99, 3], 4] - also changed!

# Deep copy for nested structures
import copy
original = [1, [2, 3], 4]
deep = copy.deepcopy(original)
deep[1][0] = 99
print(original)  # [1, [2, 3], 4] - unchanged!

"""
Shopping list manager using list operations.
"""

def display_list(items):
    if not items:
        print("  (empty)")
        return
    for i, item in enumerate(items, 1):
        print(f"  {i}. {item}")

shopping_list = []

# Add items
shopping_list.extend(["Milk", "Bread", "Eggs", "Butter", "Cheese"])

print("Shopping List:")
display_list(shopping_list)

# Remove purchased item
shopping_list.remove("Bread")
print("\nAfter buying Bread:")
display_list(shopping_list)

# Sort alphabetically
shopping_list.sort()
print("\nSorted:")
display_list(shopping_list)

# Check if item is needed
item = "Eggs"
if item in shopping_list:
    print(f"\n✓ {item} is on the list")

# Summary
print(f"\nTotal items: {len(shopping_list)}")