While loop in Python programming language

In this tutorial, we will discuss While loop in Python programming language

A while loop in Python programming language executes a target statement repeatedly until satisfaction or test expression is true.

Declaration

The syntax of while loop

The syntax of while loop in Python programming language is given below:

while expression:
//body of while
    statement(s)

Flow diagram of while loop

In the above diagram, initially, the flow of control enters the while loop and checks test expression.

When test expression is true, the flow of control enters the body part of while loop and codes inside the body of while loop is executed.

The process continue until the test expression evaluates to false

When test expression is false, the flow of control jumps out of the body part of the while loop and executes statements below of while loop.

Examples

Program 1

To display positive numbers less than ten using while loop in Python

i=1
while i<10:
    print i
    i=i+1;

When the above code executes, it produces the following results

Program 2

count_1=10
count_2=100
while count_1<=20 and count_2>=0:
    print(count_1,count_2)
    count_1=count_1+2
    count_2=count_2+10
print("End the loop")

When the above code executes, it produces the following results

(10, 100)
(12, 110)
(14, 120)
(16, 130)
(18, 140)
(20, 150)
End the loop

Program 3

Print first ten triangular number Using while loop in Python

#Diclare two variable as int and initialize zero
sum=0
i=0
while i<=10:    #while loop test expression
    sum=sum+i   #Updating sum by i
    print sum,
    i=i+1 #updating i by 1

When the above code executes, it produces the following results

0 1 3 6 10 15 21 28 36 45 55

Program 4

To calculate and display the sum of given numbers

#add natural number 1 to n
#1+2+3+4.....+n
n=input("Enter the number for n:" )
        #To take input from user

#initialized two variable sum and count
sum=0
count=0
while count<=n:    #while loop test expression
    sum=sum+count   #Updating sum by count
    count=count+1#update count
    print ("The total is",sum) #display total

When the above code is executed, it produces the following results

Enter the number for n:7
('The total is', 0)
('The total is', 1)
('The total is', 3)
('The total is', 6)
('The total is', 10)
('The total is', 15)
('The total is', 21)
('The total is', 28)

How to use else statement in while loop

In the Python programming language, we can use optional else block with while loop same as for loop in python

The else part is excuted when the test expression in the wile loop evaluated to false

Program 1

i=0
while i<=5:
    print i, "Is less than equal to 5"
    i=i+1
else:
    print i, "Is not less than equal to 5"

When the above code executes, it produces the following results

0 Is less than equal to 5
1 Is less than equal to 5
2 Is less than equal to 5
3 Is less than equal to 5
4 Is less than equal to 5
5 Is less than equal to 5
6 Is not less than equal to 5

Python list with the while loop

Program 1

Name=['Ram','Jhon','Muru','Nilo','Mackal','Yaso'];
i=0;
while(i<=5):
    print Name[i];
    i=i+1;

When the above code is executed, it produces the following results

Ram
Jhon
Muru
Nilo
Mackal
Yaso

The name is a list in Python

Python list index starts from Zero

So while loop display 0 to 4 element in the list (i<=4)

Program 2

Name=['Ram','Jhon','Muru','Nilo','Mackal','Yaso'];
i=0;
while(i<=5):
    print Name;
    i=i+1;

When the above code is executed, it produces the following results

['Ram', 'Jhon', 'Muru', 'Nilo', 'Mackal', 'Yaso']
['Ram', 'Jhon', 'Muru', 'Nilo', 'Mackal', 'Yaso']
['Ram', 'Jhon', 'Muru', 'Nilo', 'Mackal', 'Yaso']
['Ram', 'Jhon', 'Muru', 'Nilo', 'Mackal', 'Yaso']
['Ram', 'Jhon', 'Muru', 'Nilo', 'Mackal', 'Yaso']
['Ram', 'Jhon', 'Muru', 'Nilo', 'Mackal', 'Yaso']

In this program, Python uses the name as a single (list)variable