Lesson 8.3: Tuples and Immutability

1. What is a Tuple?

A tuple is an ordered, immutable sequence of values. It works just like a list, except you cannot change it after it is created — no adding, removing, or modifying elements.

# Creating a tuple with parentheses
colors = ("red", "green", "blue")
print(colors)
print(type(colors))

# Tuples can hold mixed types
record = ("Alice", 25, 3.8, True)
print(record)

2. Creating Tuples

With Parentheses

point = (3, 7)
weekdays = ("Mon", "Tue", "Wed", "Thu", "Fri")

Without Parentheses (Tuple Packing)

# The comma is what makes it a tuple, not the parentheses
coordinates = 4, 5
print(type(coordinates))

Single-Element Tuple (The Trailing Comma)

# This is NOT a tuple - just a string in parentheses
not_a_tuple = ("hello")
print(type(not_a_tuple))

# This IS a tuple - note the trailing comma
is_a_tuple = ("hello",)
print(type(is_a_tuple))

Empty Tuple

empty = ()
also_empty = tuple()
print(len(empty))

Converting Other Sequences to Tuples

my_list = [1, 2, 3]
my_tuple = tuple(my_list)
print(my_tuple)

my_string = "abc"
char_tuple = tuple(my_string)
print(char_tuple)

3. Accessing Tuple Elements

Tuples support the same indexing and slicing as lists:

fruits = ("apple", "banana", "cherry", "date")

# Indexing
print(fruits[0])
print(fruits[-1])

# Slicing
print(fruits[1:3])

# Length
print(len(fruits))

# Membership test
print("banana" in fruits)

What You Cannot Do

fruits = ("apple", "banana", "cherry")

# These will all raise TypeError:
# fruits[0] = "avocado"    # Can't change elements
# fruits.append("date")    # No append method
# del fruits[1]            # Can't delete elements

4. Tuple Unpacking

One of the most powerful tuple features is unpacking — assigning each element to a separate variable in one line:

# Basic unpacking
point = (3, 7)
x, y = point
print(f"x = {x}, y = {y}")

# Unpacking with more values
name, age, major = ("Alice", 20, "CS")
print(f"{name} is {age}, studying {major}")

Swapping Variables

Tuple unpacking makes swapping values elegant:

a = 10
b = 20

# Swap without a temporary variable!
a, b = b, a
print(f"a = {a}, b = {b}")

Unpacking in Loops

students = [
    ("Alice", 95),
    ("Bob", 87),
    ("Carol", 92)
]

for name, score in students:
    print(f"{name}: {score}")

5. Tuple Methods

Because tuples are immutable, they have only two methods:

numbers = (1, 3, 5, 3, 7, 3)

# count() - how many times a value appears
print(numbers.count(3))

# index() - position of first occurrence
print(numbers.index(5))
print(numbers.index(3))  # first occurrence of 3

You can also use built-in functions on tuples:

nums = (10, 20, 5, 30, 15)

print(min(nums))
print(max(nums))
print(sum(nums))
print(sorted(nums))  # returns a LIST, not a tuple

6. Why Immutability Matters

At first, it may seem like tuples are just limited lists. But immutability provides real benefits:

# Tuples can be dictionary keys (lists cannot!)
locations = {
    (40.7, -74.0): "New York",
    (34.0, -118.2): "Los Angeles",
    (41.9, -87.6): "Chicago"
}

print(locations[(34.0, -118.2)])