Loops are used for the repeated execution of a code until the desired condition is met. In this tutorial, you will learn about Python
In Python, there are two types of loops only.
- While loop
- For loop
Python programming while loop
Loops are either infinite or conditional. Python
while loop keeps reiterating a block of code defined inside it until the desired condition is met.
while loop contains a boolean expression and the code inside the loop is repeatedly executed as long as the boolean expression is true.
Python while loop – Syntax
As seen in the syntax,
while loop runs till the boolean expression returns
TRUE. The statements that are executed inside while can be a single line of code or a block of multiple statements.
Flowchart of Python while loop
One key thing to be noted is that the
while loop is entry controlled, which means the loop can never run and the
while loop is skipped if the initial test returns
For example, following code inside the while loop will be never executed because the initial test will return
i = 5 while (i > 8): print ('This is while loop') i++
Here in this program
while loop won’t be executed because in initial test
i > 8 will return
FALSE as the value of
i is 5.
The infinite while loop in Python
While the loop is skipped if the initial test returns
FALSE, it is also forever repeated infinitely if the expression always returns
while loop in the following code will never exit out of the loop and the
while loop will iterate forever.
i = 5 while (i = 5): print ('Infinite loop')
In this example, the value of
i will always be 5, so the expression will always return
TRUE resulting the iteration of
while loop infinitely. The program will never stop and will continue printing ‘infinite loop’ forever.
Python while loop: Example
#program to display 1 to 9 i = 1 while (i < 10): print (i) i = i+1
This program will initially check if the value of
i is less than 10 or not. If it is
TRUE, then it will print the value of
i and the value of
i will be increased by 1. This process will be repeated until the value of
i is less than 10 i.e. 9.
Hence, it will generate the following output.
1 2 2 4 5 6 7 8 9
Python: Using If statement with while loop
Till now we discussed iterating a block of code in
while loop until a condition is met.
What if we want to impose another condition inside while loop and break out of while loop even without meeting condition in while loop expression?
For this, we can use
if else statement to check a condition and
break keyword to jump out of
while loop even without completing the expression in
Here is the example to illustrate this.
a = 1 b = 1 while (a<10): print ('Iteration',a) a = a + 1 b = b + 1 if (b == 4): break print ('While loop terminated')
This script will produce the following output.
Iteration 1 Iteration 2 Iteration 3 While loop terminated
In above program,
while loop is supposed to iterate 9 times until the value of
a is less than 10.
In the first three iterations
Iteration 2 and
Iteration 3 is printed in the console.
Until this point the value of
b both is 3, hence the
if statement is not executed. After the 3rd iteration the value of
b both becomes 4 and the expression in
if statement return
TRUE triggering the
break statement as the value of
b is equal to 4.
Hence, the flow of program jumps out of the loop before completing 9 iterations and
while loop terminated is printed out in the console.
This is all about the Python
While Loop. In the next tutorial, you will learn about Python