Overview

This article will explain how to create a for loop in one line of code and why and when using this is preferred than the standard for loop syntax.

Standard For Loop Syntax

A for loop is written with at least two lines:

for i in range(0, 3):
    print(i)

How to create a One Line For Loop

Instead of writing “print(i)” on the next line, it can be written after the colin or “:“

for i in range(0, 3): print(i)

Using a Single Line For Loop to Print Lists

A single line for loop can also print out a statement or variable that contains a casted list statement. Usually, the for loop sentence is written first and then on the next line, the statement to print out a certain result is written. In a one line for loop statement, the variable is written first and then the for loop statement.

''' Below shows the variable numbers_in_a_list is 
assigned to data that is casted within a list '''

numbers_in_a_list = [number for number in range(1, 10)]
print(numbers_in_a_list)

Using Single Line for Loops for Lambda Functions

In Python, lambda functions are written in one line to first declare variables and then a statement that uses the declared variables to perform an operation. Single line for loops are often used with lambda functions.

How to make a Lambda Function

Below shows how to make a lambda function. The word “lambda” has to be written first and then declare as much variables as needed. After declaring the variables, a colin or “:” is written and a statement to perform an operation that uses the declared variables.

addition = lambda var1, var2 : var1 + var2
print(addition(2, 3))
# Output: 5

How to use a Single Line for Loops with Lambda Functions

Single line for loops is often recommended to be used with Lambda functions where the statement is formatted in a list:

subtraction = lambda x, y : [x-y for i in range(0,4)]
print(subtraction(2,5))
# Output: [-3, -3, -3, -3]

The usual way of writing a one line for loop will not work with a lambda function because the colin or “:” would be repeated twice and then Python has trouble reading the syntax.