Python While Loop
In this tutorial, you will learn what is Python while loop and how you can use it in your code.
In This Python Lesson You’ll Learn:
What is while loop in Python?
In Python programming language a while loop is used to iterate a block of code until the given condition becomes true. Generally, in while loop, we don’t know how much time do we need to iterate.
Syntax of while Loop in Python
while test_expression: Body of while loop
Here in the above syntax of while loop test_expression runs first. Only if the test_expression becomes true then the body of while loop runs. After completing one successful iteration the test_expression checked again and if it is true then the body of while loop runs again and this process goes on until the test_expression becomes false.
Body of while loop can consist of a single line statement or a multi-line block of code. As the test_expression becomes false the control of the program passes to line right after the body of while loop.
Flowchart of while loop
Here you can see first that checked is test_expression and if it is false the while loop will be exit and all control shifts to the very next line of the loop but in case if test_expression is true the body of while loop starts to execute and it will continue until the test_expression becomes false.
Example of Python while Loop
# This while loop example shows the addition of natural numbers # Natural numbers are like = 1+2+3+...+n n = 12 # Here we initialize sum and counter sum = 0 x = 1 while x <= n: sum = sum + x x = x+1 # counter will increament print("The sum of natural numbers is", sum)
The sum of natural number is 78
In the above example our python while loop continues to run as long as our variable x is less or equal to variable n(12).
Remember: We must increase x = x+1 counter variable. This is the most important work unless the loop never ends and continue running infinity until all the memory exhausts.
while loop with else
Python offers an optional else statement with the while loop as of with the for loop. But the else block will only run if the text_expression in a while loop becomes false.
Example of while loop with else statement
#Python while loop with else statement counter = 0 while counter < 3: print("Body of while loop increment by 1 on each iteration") counter = counter + 1 else: print("It is else block")
after the above code executes the following results shows:
Body of while loop increment by 1 on each iteration Body of while loop increment by 1 on each iteration Body of while loop increment by 1 on each iteration It is else block