Python Comprehensions

In this article, we shall see how comprehension can be done in the data structures of Python like lists, dictionaries, set, and generators.

Comprehension provides a precise way of writing a program in Python. It reduces the code size without affecting its easy readability.

So, here we will discuss the following comprehensions -

1. List Comprehension
2. Dictionary Comprehension
3. Set Comprehension
4. Generator Comprehension

List Comprehension

We know that the elements of a list are enclosed in square brackets and it can hold values of multiple data types.

In the program given below, we will take out the even numbers from the list.

Let's see the below example of list.

Example -

Output-

The elements of list2 are : [20, 24, 30, 40, 44]

Here we have specified the elements of list1, and then used for loop to take each element and checked using modulus operator that it is divisible by 2 or not.

In the program given below, we performed the same using list comprehension.

Example - 2-Using List Comprehension

Output-

The elements obtained using list comprehension are : [20, 24, 30, 40, 44]

Here, we can observe that we provided the comprehension in list2 where we used for loop and decision making in a single line.

The next program is based on obtaining the cube of all elements present in list1.

Example - 3

Output-

The cube of the elements present in list1 is:  [8, 27, 64, 125, 216, 343, 512, 729, 1000]

We used the append() method and stored the cube of each element in list2 and then displayed it.

We co do the same thing using list comprehension-

Example - 4-Using List Comprehension

Output-

The cube of the elements obtained by list comprehension is:  [8, 27, 64, 125, 216, 343, 512, 729, 1000]

Dictionary Comprehension

We all know that dictionary uses key-value pairs, let us have a look at the program of displaying these pairs.

Example -

Output-

The resultant dictionary would be:  {'Apple': 'Red', 'Bananas': 'Yellow', 'Custard Apple': 'Green', 'Pineapple': 'Brown', 'Blueberries': 'Violet'}

In the next program, the same thing is implemented using comprehension

Example - 2-Usind Dictionary Comprehension

Output-

The resultant dictionary using comprehension would be:  {'Apple': 'Red', 'Bananas': 'Yellow', 'Custard Apple': 'Green', 'Pineapple': 'Brown', 'Blueberries': 'Violet'}

Here, we can observe that we provided the comprehension in result_dict where we have given the expression for displaying the key-value pairs from the lists fruits and color.

Set Comprehension

Set is used to display the unique elements from a given collection. Let's obtain the square of all elements of list using set.

Example - 1

Output-

The square of the numbers present in list1 is:  {64, 4, 36, 100, 9, 16, 49, 81, 25}

In the program given below, we have done the same thing using comprehension.

Example - 2- Using set comprehension

Output-

The square of the numbers obtained through set comprehension:  {64, 4, 36, 100, 9, 16, 49, 81, 25}

We have taken each element from list1 and provided the expression in result_set for calculating the square of these elements.

Generator Comprehension

The generators are the quite similar to functions. It uses the yield keyword to generate a value. Let us see how comprehension can be used here.

Example -

Output-

The element which is even in list1 is:  12
The element which is even in list1 is:  16
The element which is even in list1 is:  20
The element which is even in list1 is:  24
The element which is even in list1 is:  28
The element which is even in list1 is:  30

On executing the program, it displays the even elements from list1.