Lists

# Empty list
items = []

# List with values
numbers = [1, 2, 3, 4, 5]
names = ["Alice", "Bob", "Charlie"]
mixed = [42, "hello", True, 3.14, None]

# From other iterables
letters = list("hello")        # ['h', 'e', 'l', 'l', 'o']
nums = list(range(1, 6))      # [1, 2, 3, 4, 5]

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

print(fruits[0])    # apple
print(fruits[2])    # cherry
print(fruits[-1])   # elderberry (last item)
print(fruits[-2])   # date (second to last)

nums = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

print(nums[2:5])    # [2, 3, 4] — index 2 up to (not including) 5
print(nums[:3])     # [0, 1, 2] — from start
print(nums[7:])     # [7, 8, 9] — to end
print(nums[::2])    # [0, 2, 4, 6, 8] — every other element
print(nums[::-1])   # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0] — reversed

fruits = ["apple", "banana"]

fruits.append("cherry")          # add to end → ['apple', 'banana', 'cherry']
fruits.insert(1, "blueberry")    # insert at index → ['apple', 'blueberry', 'banana', 'cherry']
fruits.extend(["date", "fig"])   # add multiple → [..., 'date', 'fig']

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

fruits.remove("banana")   # removes FIRST occurrence → ['apple', 'cherry', 'banana', 'date']
popped = fruits.pop()     # removes and returns last → 'date'
popped = fruits.pop(0)    # removes and returns at index → 'apple'
del fruits[0]             # delete by index
fruits.clear()            # remove everything → []

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

colors[1] = "yellow"              # ['red', 'yellow', 'blue']
colors[0:2] = ["pink", "purple"]  # ['pink', 'purple', 'blue']

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

print(len(numbers))        # 8
print(min(numbers))        # 1
print(max(numbers))        # 9
print(sum(numbers))        # 31
print(numbers.count(1))    # 2 (how many times 1 appears)
print(numbers.index(5))    # 4 (index of first occurrence)
print(5 in numbers)        # True
print(10 in numbers)       # False

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

# Sort in place (modifies the list)
numbers.sort()
print(numbers)  # [1, 1, 3, 4, 5, 9]

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

# sorted() returns a new list (original unchanged)
original = [3, 1, 4, 1, 5]
ordered = sorted(original)
print(original)  # [3, 1, 4, 1, 5] — unchanged
print(ordered)   # [1, 1, 3, 4, 5]

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

# Sort by length
words.sort(key=len)
print(words)  # ['date', 'apple', 'banana', 'cherry']

# Sort objects by a property
users = [
    {"name": "Charlie", "age": 30},
    {"name": "Alice", "age": 25},
    {"name": "Bob", "age": 28}
]

users.sort(key=lambda u: u["age"])
print([u["name"] for u in users])  # ['Alice', 'Bob', 'Charlie']

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

# Simple loop
for fruit in fruits:
    print(fruit)

# With index
for i, fruit in enumerate(fruits):
    print(f"{i}: {fruit}")

# enumerate with custom start
for i, fruit in enumerate(fruits, start=1):
    print(f"{i}. {fruit}")

# 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]

# Transform and filter
names = ["Alice", "Bob", "Charlie", "Dave"]
long_upper = [name.upper() for name in names if len(name) > 3]
print(long_upper)  # ['ALICE', 'CHARLIE', 'DAVE']

# Comprehension — great for simple transformations
prices = [10, 25, 5, 40]
with_tax = [price * 1.08 for price in prices]

# Loop — better when logic is complex or has side effects
results = []
for price in prices:
    if price > 20:
        discounted = price * 0.9
        results.append(round(discounted, 2))

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

print(matrix[0])      # [1, 2, 3] — first row
print(matrix[1][2])   # 6 — row 1, column 2

# Iterate over all elements
for row in matrix:
    for cell in row:
        print(cell, end=" ")
    print()

# Flatten with a comprehension
flat = [cell for row in matrix for cell in row]
print(flat)  # [1, 2, 3, 4, 5, 6, 7, 8, 9]

original = [1, 2, 3]
reference = original       # NOT a copy!
reference.append(4)
print(original)            # [1, 2, 3, 4] — modified!

# Shallow copy (works for simple lists)
copy1 = original.copy()
copy2 = original[:]
copy3 = list(original)

# Deep copy (needed for nested lists)
import copy
nested = [[1, 2], [3, 4]]
deep = copy.deepcopy(nested)
deep[0].append(99)
print(nested)  # [[1, 2], [3, 4]] — unaffected

# Basic unpacking
first, second, third = [1, 2, 3]

# Star unpacking — collect the rest
first, *middle, last = [1, 2, 3, 4, 5]
print(first)   # 1
print(middle)  # [2, 3, 4]
print(last)    # 5

# Swap values
a, b = 1, 2
a, b = b, a
print(a, b)  # 2, 1

scores = [85, 42, 91, 67, 73, 55, 88]
passing = [s for s in scores if s >= 70]
print(passing)  # [85, 91, 67, 73, 88]

names = ["Alice", "Bob", "Charlie"]
scores = [95, 87, 92]

paired = list(zip(names, scores))
print(paired)  # [('Alice', 95), ('Bob', 87), ('Charlie', 92)]

# Create a dict from two lists
score_map = dict(zip(names, scores))
print(score_map)  # {'Alice': 95, 'Bob': 87, 'Charlie': 92}

items = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3]
unique = list(dict.fromkeys(items))
print(unique)  # [3, 1, 4, 5, 9, 2, 6]

def chunk(lst, size):
    return [lst[i:i + size] for i in range(0, len(lst), size)]

print(chunk([1, 2, 3, 4, 5, 6, 7], 3))
# [[1, 2, 3], [4, 5, 6], [7]]