Tuples

Updated Oct 28, 2019 ·

Overview

Tuples are immutable containers that hold data like lists. However, unlike lists, we cannot add, remove, or change their elements. This makes tuples safer for storing data that should not be modified.

Tuples can be created by grouping elements with parentheses. We can then access elements using their index.

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

print(fruits[0])  # apple
print(fruits[2])  # cherry

Zipping Tuples

The zip function lets us pair elements from multiple lists into tuples. For example, we can match cookie popularity in two countries:

us_cookies = ["Chips Ahoy", "Oreo", "Nilla"]
in_cookies = ["Treat", "Hide & Seek", "Oreo"]

top_pairs = list(zip(us_cookies, in_cookies))
print(top_pairs)

Output:

[('Chips Ahoy', 'Treat'), ('Oreo', 'Hide & Seek'), ('Nilla', 'Oreo')]

When two lists (or tuples) don’t have the same number of elements, the zip function will only pair up elements until the shortest sequence ends. Extra elements in the longer list are ignored.

us_cookies = ["Chips Ahoy", "Oreo", "Nilla", "Amos"]
in_cookies = ["Treat", "Hide & Seek", "Oreo"]

top_pairs = list(zip(us_cookies, in_cookies))
print(top_pairs)

Output:

[('Chips Ahoy', 'Treat'), ('Oreo', 'Hide & Seek'), ('Nilla', 'Oreo')]

Notice that "Amos" from us_cookies is not included because in_cookies has only 3 elements.

Unpacking Tuples

Tuple unpacking assigns elements of a tuple to variables in one step.

top_pairs = [ ('Chips Ahoy', 'Treat'), 
              ('Oreo', 'Hide & Seek'), 
              ('Nilla', 'Oreo') ] 

us_num_1, in_num_1 = top_pairs[0]
print(us_num_1, in_num_1)

Output:

Chips Ahoy Treat

Unpacking in Loops

We can also unpack tuples directly in loops to handle multiple values at once.

top_pairs = [ ('Chips Ahoy', 'Treat'), 
              ('Oreo', 'Hide & Seek'), 
              ('Nilla', 'Oreo') ] 

for us_cookie, in_cookie in top_pairs:
    print(us_cookie, in_cookie)

Output:

Chips Ahoy Treat
Oreo Hide & Seek
Nilla Oreo

Each element of top_pairs is itself a tuple with 2 items. For example, the first element is a pair:

('Chips Ahoy', 'Treat')

Using the for loop, it "unpacks" the element into two variables and executes the print statement.

us_cookie = 'Chips Ahoy'
in_cookie = 'Treat'

Enumerating Positions

The enumerate function creates tuples of index and element. This helps track positions in a list.

top_pairs = [ ('Chips Ahoy', 'Treat'), 
              ('Oreo', 'Hide & Seek'), 
              ('Nilla', 'Oreo') ] 

for index, item in enumerate(top_pairs):
    us_cookie, in_cookie = item
    print(index, us_cookie, in_cookie)

Output:

0 Chips Ahoy Treat
1 Oreo Hide & Seek
2 Nilla Oreo

As we have seen, a tuple can be created with parentheses, zip, enumerate, or even a trailing comma. Always check how they are created because even a single stray comma can cause unexpected bugs.