Tuples

A tuple is like a list that cannot be changed after it is created. Tuples use round brackets.

point = (3, 4)
colour = (255, 128, 0)
person = ("Asha", 21, "Mumbai")

print(point[0], point[1])
print(person[-1])
print(len(colour))

Tuples are immutable

point = (3, 4)
point[0] = 10

You can still make a new tuple from an old one: point = (10, point[1]).

Why use a tuple?

• Safety: data that should not change (a date, a coordinate, an RGB colour) cannot be changed by accident.
• Dictionary keys: tuples can be keys in a dictionary; lists cannot.
• Meaning: by convention, a tuple holds a fixed set of different things (name, age, city), while a list holds many things of the same kind.

Packing and unpacking

Writing values separated by commas packs them into a tuple; assigning a tuple to several names unpacks it:

location = 19.07, 72.88          # packing (brackets are optional)
lat, lon = location              # unpacking
print(lat, lon)

name, age, city = ("Leo", 30, "London")
print(f"{name} ({age}) lives in {city}")

The number of names must match the number of items, unless you use * to collect the rest:

first, *rest = [1, 2, 3, 4, 5]
print(first, rest)

*start, last = "python"
print(start, last)

Returning several values

A function can return a tuple, which the caller unpacks. It looks like returning several values at once:

def min_max(numbers):
    return min(numbers), max(numbers)

low, high = min_max([7, 2, 9, 4])
print(low, high)

A one-item tuple

The comma makes a tuple, not the brackets:

not_a_tuple = (5)
a_tuple = (5,)
print(type(not_a_tuple), type(a_tuple))

Tuple methods

Tuples only have two methods, because they cannot change:

grades = ("A", "B", "A", "C", "A")
print(grades.count("A"))
print(grades.index("C"))