Visualize Python zip function

If you already understand how zip() and zip_longest() work just by looking at the examples in the first section, you probably don't need this visualization. But if you're curious to see them in action—or just enjoy visual explanations—stick around!

Examples

Go through the examples below and see if you can understand how the zip() and zip_longest() functions work. Expand the output to see if it matches your expectations.

Example 1: Pairing Elements with zip()

from itertools import zip_longest

numbers_1 = [1, 2, 3, 4]
numbers_2 = [5, 6]

paired = list(zip(numbers_1, numbers_2))
print(paired)

Output

[(1, 5), (2, 6)]

Example 2: Pairing Elements with zip_longest()

from itertools import zip_longest

numbers_1 = [1, 2, 3, 4]
numbers_2 = [5, 6]

paired = list(zip_longest(numbers_1, numbers_2, fillvalue=0))

print(paired)

Output

  [(1, 5), (2, 6), (3, 0), (4, 0)] 

Visualizing zip()

The zip() function takes two or more iterables and returns an iterator of tuples. Each tuple contains elements from the input iterables at the same index. If the input iterables are of different lengths, zip() stops creating tuples when the shortest iterable is exhausted.

This is better understood with a visualization. The following interactive model shows how zip() works. Use the + and - buttons to add or remove elements from the input lists. Use the Add and Remove buttons to add or remove lists. The demo supports only numbers and the size is constrained to keep the animation smooth. The "Code Representation" section shows the corresponding code for your current configuration. Click "Play Animation" to see how the zip() function works with the current configuration. After the animation, you can see the output of the zip() function in the "Output" section. You can also click Reset to go back to the initial state.

iterable0 = [1, 2, 3]
iterable1 = [1, 2, 3]
zipped = zip(
    iterable0,
    iterable1
)
print(list(zipped))

Visualizing zip_longest()

The zip_longest() works almost like zip(), but it continues until the longest iterable is exhausted. It fills in missing values with a specified fillvalue (default is None). This is useful when you want to pair elements from iterables of different lengths without losing any data. Play around with the following demo to see how zip_longest() works. The demo is similar to the one for zip(), but it includes an additional input field for the fillvalue.

from itertools import(
zip_longest)

iterable0 = [1, 2, 3]
iterable1 = [1, 2, 3]

zipped = zip_longest(
    iterable0,
    iterable1,
    fillvalue=0
)
print(list(zipped))

A Realistic Example: Transpose a Matrix

The zip() function is often used to transpose a matrix. This means converting rows into columns and vice versa. Here's how you can do it:

def transpose(matrix):
    return list(map(list, zip(*matrix)))

matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

transposed = transpose(matrix)
for row in transposed:
    print(row)

Output

The first row [1, 2, 3] in the input becomes the first column [1, 4, 7] in the output, the second row [4, 5, 6] becomes the second column [2, 5, 8], and so on.

[1, 4, 7]
[2, 5, 8]
[3, 6, 9]

Another Realistic Example: Clubbing Values

zip() and zip_longest() can be used with iterables with different data types, not just numbers like in the visualization demos. Here is a realistic example of how zip() can be used.

from itertools import zip_longest

raw_sensor_data = [
    ("12:00", 20.1),
    ("12:02", 20.3),  # No reading at 12:01
    ("12:04", 20.2)   # No reading at 12:03
]

expected_timestamps = ["12:00", "12:01", "12:02", "12:03", "12:04"]

# Convert to dictionary for easy lookup
reading_dict = dict(raw_sensor_data)

# Fill missing values (we're not using zip_longest. Guess why?)
readings = [reading_dict.get(t, "Missing") for t in expected_timestamps]

# Pairing timestamps with readings
paired = list(zip(expected_timestamps, readings))
print(paired)

Output

[
    ('12:00', 20.1),
    ('12:01', 'Missing'),
    ('12:02', 20.3),
    ('12:03', 'Missing'),
    ('12:04', 20.2)
]