Lists and Tuples

Lists and tuples are Python's most fundamental sequence data structures. Both store ordered collections of items, but they differ in mutability: lists can be changed after creation, tuples cannot.

Lists

A list is an ordered, mutable collection defined with square brackets:

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

Accessing Items

Items are accessed by zero-based index:

fruits = ["apple", "banana", "cherry"]
print(fruits[0])    # apple
print(fruits[-1])   # cherry (negative index from end)
print(fruits[1:3])  # ['banana', 'cherry'] (slicing)

Modifying Lists

fruits = ["apple", "banana", "cherry"]
fruits[1] = "blueberry"          # replace item
fruits.append("mango")           # add to end
fruits.insert(1, "avocado")      # insert at index
fruits.remove("apple")           # remove by value
popped = fruits.pop()            # remove and return last item
popped_at = fruits.pop(0)        # remove and return at index

List Methods

nums = [3, 1, 4, 1, 5, 9]
nums.sort()             # sorts in place
nums.reverse()          # reverses in place
print(len(nums))        # 6 — number of items
print(nums.count(1))    # 2 — count occurrences
print(nums.index(4))    # index of first occurrence

List Comprehensions

A concise way to build lists:

squares = [x ** 2 for x in range(1, 6)]
print(squares)   # [1, 4, 9, 16, 25]

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

Tuples

A tuple is an ordered, immutable collection defined with parentheses:

point = (3, 7)
rgb = (255, 128, 0)
single = (42,)   # trailing comma required for single-element tuple

You access tuple items the same way as lists, but you cannot modify them:

point = (3, 7)
print(point[0])   # 3
# point[0] = 10  # TypeError: tuple is immutable

When to Use Tuples vs Lists

Use tuples for data that should not change — coordinates, RGB colors, database records returned from a query. Use lists when you need to add, remove, or reorder items.

Tuple Unpacking

coordinates = (10, 20, 30)
x, y, z = coordinates
print(x, y, z)   # 10 20 30

Checking Membership

fruits = ["apple", "banana", "cherry"]
print("banana" in fruits)    # True
print("grape" not in fruits) # True