List Comprehension in python with example

In this post, we will learn about what is list comprehension, Syntax of list comprehension, list comprehension with an if statement, list comprehension with the if-else statement, nested list comprehension, and so on.

So let’s start learning from the very basics

What is List Comprehension?

List comprehension is short-hand to create a new list from an existing list or iterable.

Basically, List comprehension helps you to create a new list from an existing list in just one line.

NOTE: You can also create a completely new list using list comprehension.

Now let us create a list of squares from 1 to 10 without using list comprehension and with using list comprehension for your understanding.

Without using list comprehension:

sq_list = []

for i in range(1,11):
    sq_list.append(i**2)

print(sq_list)

Output:

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

With using list comprehension:

sq_list = [i**2 for i in range(1,11)]
print(sq_list)

Output:

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

Creating a List of squares from 1 to 10 using list comprehension is much easier and simpler because we did it in just one line whereas we write 3-4 lines of code without using list comprehension.

Syntax of List Comprehension

my_list = [expression for i in iterable if condition == True]

expressionmeans what you want to append in the list.

For Example:

List Comprehension with if-statement

Create a list of even numbers from existing list my_list = [45,12,67,8,2,6,90,13,15]

my_list = [45,12,67,8,2,6,90,13,15]

my_list2 = [i for i in my_list if i%2 == 0]

print(my_list2)

Output:

[12, 8, 2, 6, 90]

Examples for practice

Filter integer or float numbers from the list

l1 = ['harsh',3,'roy','nil',1.1,25,2.1]

l2 = [i for i in l1 if (type(i) == int or type(i) == float)]

print(l2)

Output:

[3, 1.1, 25, 2.1]

Create a list that contains the first character of an existing list.

my_fruit = ['Apple','Banana','Orange','Mango']

my_fruit2 = [i[0] for i in my_fruit]

print(my_fruit2)

Output:

['A', 'B', 'O', 'M']

List Comprehension with if-else statement

Syntax of List comprehension with if-else statement

Example:

mixed_list = ['Apple','Banana',12,15,7,2,3,'Orange','Mango']

# if type is equal to int then append square of the number
# otherwise append first character of string
 
mixed_list2 = [i**2 if type(i) == int else i[0] for i in mixed_list]
print(mixed_list2)

Output:

['A', 'B', 144, 225, 49, 4, 9, 'O', 'M']

Nested List Comprehension

In nested List comprehension we append the whole list.

l2 = [[i for i in range(3)] for j in range(3)]
print(l2) 

Output:

[[0, 1, 2], [0, 1, 2], [0, 1, 2]]