Python Dictionary Comprehension: A Simple Explaination

You may be familiar with list comprehension, but did you know that you can do the same thing, but with Python dictionaries? It’s been around since 2001!

Here, we’re going to discuss what dictionary comprehension is and how you can use it in your code.

Article Contents

• Dictionary comprehension structure

• Dictionary Comprehension Use Cases

• Examples of dictionary comprehension

Dictionary comprehension structure

If you’re already familiar with list comprehension, you’re in luck - dictionary comprehension is very similar to list comprehension.

The idea is the same: short syntax when you want to create a new dictionary.

As a reminder, list comprehension is structured as such:

list_comp = [value for value in iterable]

Similarly, dictionary comprehension is structured nearly the same way:

dict_comp = {key : value for variable in iterable}

Where key is the key(s) in your dictionary and value are your associated values. Following this is a for loop, which you’ll be iterating over.

So, instead of declaring a dictionary outright:

square_dict = {1 : 1, 2 : 4, 3 : 9, 4 : 16, 5 : 25}

We can write it as such:

square_dict = {num : num * num for num in range(1, 6)}

When you want to use dictionary comprehension

There’s a few instances where you may opt to use this syntax:

• Filtering Dictionary Entries: If you need to filter out entries in an existing dictionary.

• Applying a Function to Dictionary Values: Dictionary comprehension allows for a clean way to do this.

• Inverting a Dictionary: There may be instances where you want to flip the keys and values. Using dictionary comprehension is a one line solution to this problem!

Personally, I use dictionary comprehension to clean up the code so it’s easier to read.

Examples of dictionary comprehension

While providing use cases is pretty helpful, it may be better to see the code. Below are 3 examples on when you may want to use this method instead.

The first example is to create a dictionary mapping each character in a string to its ASCII value:

In the instance you want to merge two dictionaries and perform a calculation on the values from each, you can approach it two ways, as shown below:

Hope this helps!

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