Power of zip() in Python

Topics covered

1. Why use zip?
2. Unzipping
3. Solve a competitive interview question

Why use zip?

zip() allows you to map the same index of multiple iterables.

Syntax of zip

zip(*iterables)

Let’s look at an example.

x = [1, 2, 3]
y = [4, 5, 6]

mapping = zip(x, y)
print(mapping)

If you run the above snippet, it will return you something like this.

<zip object at 0x1033d7d08>

As you can see, when you print(mapping), it returns a zip object. This is an iterator object that consists of tuples. To check out its contents, let’s convert it to a list.

print(list(mapping))

This snippet produces the following result.

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

Unzipping

Now how to unzip? You can do that with the * operator. Let’s convert our mapping variable back to its components.

x,y = zip(*mapping)

print(x)
print(y)

This in turn assigns tuples to x and y variables.

(1, 2, 3) # Value of x
(4, 5, 6) # Value of y

As I mentioned earlier, zip() creates an iterator of tuples. Therefore when we unpack, we get our x and y values back as tuples. You can use the list() method to convert them back to lists.

Solve a competitive interview question

Write a function to map all elements of the same index for the following list.

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

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

The function should take in the input_lst and return the output_lst.

If you are able to solve it, make sure to let me know on Twitter.