Data Structures

Lists, tuples, dictionaries, and sets - Python's built-in data structures.

Lists

Ordered, mutable collections.
Can contain mixed data types.
Access elements by index (starting at 0).
Support slicing, appending, and more.

# Creating lists
fruits = ["apple", "banana", "cherry"]
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", 3.14, True]

# Accessing elements
print(fruits[0])      # apple
print(fruits[-1])     # cherry (last item)

# Slicing
print(numbers[1:4])   # [2, 3, 4]

# Modifying
fruits.append("orange")
fruits.insert(1, "mango")
fruits.remove("banana")
print(fruits)

List Methods

append(): Add item to end
insert(): Add item at position
remove(): Remove first occurrence
pop(): Remove and return item
sort(): Sort list in place
reverse(): Reverse list in place

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

numbers.append(9)
print(numbers)        # [3, 1, 4, 1, 5, 9]

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

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

last = numbers.pop()
print(last)           # 1
print(numbers)        # [9, 5, 4, 3, 1]

Tuples

Ordered, immutable collections.
Faster than lists for read-only data.
Use parentheses () instead of brackets [].
Support unpacking for multiple assignment.

# Creating tuples
point = (10, 20)
rgb = (255, 128, 0)

# Accessing
print(point[0])       # 10

# Unpacking
x, y = point
print(x, y)           # 10 20

# Tuples are immutable
# point[0] = 15       # Error!

# Single element tuple needs comma
single = (42,)

Dictionaries

Key-value pairs (like a real dictionary).
Keys must be unique and immutable.
Fast lookup by key.
Use curly braces {} with key:value pairs.

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

# Accessing values
print(person["name"])        # Alice
print(person.get("age"))     # 25

# Adding/modifying
person["email"] = "alice@example.com"
person["age"] = 26

# Looping
for key, value in person.items():
    print(f"{key}: {value}")

Sets

Unordered collection of unique elements.
No duplicates allowed.
Fast membership testing.
Support mathematical set operations.

# Creating sets
fruits = {"apple", "banana", "cherry"}
numbers = {1, 2, 3, 3, 4}  # Duplicates removed
print(numbers)  # {1, 2, 3, 4}

# Adding/removing
fruits.add("orange")
fruits.remove("banana")

# Set operations
a = {1, 2, 3, 4}
b = {3, 4, 5, 6}

print(a | b)  # Union: {1, 2, 3, 4, 5, 6}
print(a & b)  # Intersection: {3, 4}
print(a - b)  # Difference: {1, 2}

List Comprehensions

Concise way to create lists.
Can include conditions.
More readable than traditional loops.

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

# With 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 strings
words = ["hello", "world"]
upper = [w.upper() for w in words]
print(upper)  # ['HELLO', 'WORLD']