Tuples

We already know lists. A list can grow, shrink, and change: we can append, remove, and modify elements whenever we want. But sometimes we want a collection that cannot change. This is a tuple

coordinates = (10, 20)
print(coordinates)

Output (10, 20)

A tuple looks like a list, but with parentheses () instead of square brackets []. The big difference? We cannot modify it after creation

coordinates = (10, 20)
coordinates[0] = 99

Run it. Python will scream at us with a TypeError: 'tuple' object does not support item assignment. In other words: "you can't change me"

Why would we ever want something we can't change? Well, sometimes that's the whole point. Think about a date of birth. Tommy Vercetti was born on a specific day. That date should never change. If we accidentally write code that tries to modify it, we want Python to stop us

birthday = (1951, 7, 15)
print(birthday)

Another example: GPS coordinates. Vice City is at a fixed location. It doesn't move

vice_city = (25.7617, -80.1918)
print(vice_city)

We can read elements from a tuple, just like a list, using an index

player = ("Tommy Vercetti", 100, "Vice City")
print(player[0])
print(player[1])
print(player[2])

Output

Tommy Vercetti
100
Vice City

len() works too

player = ("Tommy Vercetti", 100, "Vice City")
print(len(player))

Output 3

One of the coolest things about tuples is unpacking. Instead of using indexes, we can grab all values at once

player = ("Tommy Vercetti", 100, "Vice City")

name, health, city = player
print(name)
print(health)
print(city)

Output

Tommy Vercetti
100
Vice City

We created three variables in one line. Python took the first element and put it in name, the second in health, the third in city. The number of variables on the left must match the number of elements in the tuple

a, b = (10, 20)
print(a)
print(b)

Output

10
20

This is the same unpacking we saw in .items() when looping through dictionaries. Now you know where it comes from

We can also loop through a tuple, just like a list

heroes = ("Shrek", "Fiona", "Donkey")
for hero in heroes:
    print(hero)

Output

Shrek
Fiona
Donkey

Mission: Star Chart

The station's navigation computer stores each star system as a tuple of (name, distance, planets), all of them in a list named systems

Loop over the list and unpack each tuple into three variables: name, distance, planets
Print each system as name: distance ly, planets planets, for example Sol: 0 ly, 8 planets (ly = light years)
After the loop, print Total planets: then the sum of all the planets

Output

Sol: 0 ly, 8 planets
Alpha: 4 ly, 3 planets
Vega: 25 ly, 5 planets
Total planets: 16