Python While Loop

Python While Loop

Python While Loop is used to execute a set of statements repeatedly based on the output of a boolean expression. While Loop is one the Looping statements available in Python programming.

In this tutorial, we shall learn how to write a while loop in Python program, and some the scenarios where while loop is used, with the help of example programs.

Syntax – While Loop

The syntax of while loop is given below.

while boolean_expression:
    statement(s)

The statements inside the while loop have to be indented as shown in the syntax. Usually when using a while loop, there can be many variables involved in the boolean expression. The variables’ initialization and update has to be taken care by the programmer.

Example 1: Python While Loop

In the following Python program, we will use while loop and print numbers from 0 to 3.

Python Program

a = 4

i = 0
while i<a:
	print(i)
	i+=1
Run this program

Output

0
1
2
3

Let us analyze this example. We have used i and a in the boolean expression and during the loop a remains constant and i kind of changes with every loop iteration. So, for every iteration, i increments and reaches a value where the boolean expression becomes false and the control comes out to the loop.

Programmer has to take care that the while loop breaks at some point in the execution. Else, it may iterate indefinitely, which may not be desired all the times.

Example 2: While Loop with Break Statement

You can break the while loop prematurely before the boolean expression becomes false. This can be done using break keyword.

In the following example, we will break the loop prematurely using a break statement.

Python Program

a = 4

i = 0
while i<a:
	print(i)
	i+=1
	if i>1:
		break
Run this program

Output

0
1

During the iteration, when i becomes 2, i>1 returns True, executing break statement. And therefore the execution of while loop is wrapped up.

Example 3: While Loop with Continue

You can skip executing an iteration of while loop using continue keyword.

In this example, we will skip the executing of statements in while loop when i=2. While loop continues with the next iterations.

Python Program

a = 4

i = 0
while i<a:
	if i==2:
		i+=1
		continue
	print(i)
	i+=1
	
Run this program

Output

0
1
3

Observe that we taken care of updating i when we are skipping an iteration. If you do not update i when you are skipping, your while loop may enter infinite loop.

Summary

In this tutorial of Python Examples, we have learned how to write and use while loop, use break and continue statements with while loop, with the help of well detailed examples.