Python While Loops

In coding, loops are designed to execute a specified code block repeatedly. We’ll learn how to construct a while loop in Python, the syntax of a while loop, loop controls like break and continue, and other exercises in this tutorial.

Introduction of Python While Loop

In this article, we are discussing while loops in Python. The Python while loop iteration of a code block is executed as long as the given Condition, i.e., conditional_expression, is true.

If we don’t know how many times we’ll execute the iteration ahead of time, we can write an indefinite loop.

Syntax of Python While Loop

Now, here we discuss the syntax of the Python while loop. The syntax is given below –

Statement  

while Condition:  

        Statement

The given condition, i.e., conditional_expression, is evaluated initially in the Python while loop. Then, if the conditional expression gives a boolean value True, the while loop statements are executed. The conditional expression is verified again when the complete code block is executed. This procedure repeatedly occurs until the conditional expression returns the boolean value False.

• The statements of the Python while loop are dictated by indentation.
• The code block begins when a statement is indented & ends with the very first unindented statement.
• Any non-zero number in Python is interpreted as boolean True. False is interpreted as None and 0.

Example

Now we give some examples of while Loop in Python. The examples are given in below –

Program code 1:

Now we give code examples of while loops in Python for printing numbers from 1 to 10. The code is given below –

i=1  

while i<=10:  

    print(i, end=' ')  

    i+=1

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -1 2 3 4 5 6 7 8 9 10

Program Code 2:

Now we give code examples of while loops in Python for Printing those numbers divisible by either 5 or 7 within 1 to 50 using a while loop. The code is given below –

i=1  

while i<51:  

    if i%5 == 0 or i%7==0 :  

        print(i, end=' ')  

    i+=1

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -5 7 10 14 15 20 21 25 28 30 35 40 42 45 49 50

Program Code:

Now we give code examples of while loops in Python, the sum of squares of the first 15 natural numbers using a while loop. The code is given below –

# Python program example to show the use of while loop   

  

num = 15  

  

# initializing summation and a counter for iteration  

summation = 0  

c = 1  

  

while c <= num: # specifying the condition of the loop  

    # begining the code block  

    summation = c**2 + summation  

    c = c + 1    # incrementing the counter  

  

# print the final sum  

print("The sum of squares is", summation)

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -The sum of squares is 1240

Provided that our counter parameter i gives boolean true for the condition, i less than or equal to num, the loop repeatedly executes the code block i number of times.

Next is a crucial point (which is mostly forgotten). We have to increment the counter parameter’s value in the loop’s statements. If we don’t, our while loop will execute itself indefinitely (a never-ending loop).

Finally, we print the result using the print statement.

Exercises of Python While Loop

Prime Numbers and Python While Loop

Using a while loop, we will construct a Python program to verify if the given integer is a prime number or not.

Program Code:

Now we give code examples of while loops in Python for a number is Prime number or not. The code is given below –

num = [34, 12, 54, 23, 75, 34, 11]    

  

def prime_number(number):  

    condition = 0  

    iteration = 2  

    while iteration <= number / 2:  

        if number % iteration == 0:  

            condition = 1  

            break  

        iteration = iteration + 1  

  

    if condition == 0:  

        print(f"{number} is a PRIME number")  

    else:  

        print(f"{number} is not a PRIME number")  

for i in num:  

    prime_number(i)

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -34 is not a PRIME number 12 is not a PRIME number 54 is not a PRIME number 23 is a PRIME number 75 is not a PRIME number 34 is not a PRIME number 11 is a PRIME number

2. Armstrong and Python While Loop

We will construct a Python program using a while loop to verify whether the given integer is an Armstrong number.

Program Code:

Now we give code examples of while loops in Python for a number is Armstrong number or not. The code is given below –

n = int(input())  

n1=str(n)  

l=len(n1)  

temp=n  

s=0  

while n!=0:  

    r=n%10  

    s=s+(r**1)  

    n=n//10  

if s==temp:  

    print("It is an Armstrong number")  

else:  

    print("It is not an Armstrong number ")

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -342 It is not an Armstrong number

Multiplication Table using While Loop

In this example, we will use the while loop for printing the multiplication table of a given number.

Program Code:

In this example, we will use the while loop for printing the multiplication table of a given number. The code is given below –

num = 21        

counter = 1      

# we will use a while loop for iterating 10 times for the multiplication table        

print("The Multiplication Table of: ", num)      

while counter <= 10: # specifying the condition  

    ans = num * counter      

    print (num, 'x', counter, '=', ans)      

    counter += 1 # expression to increment the counter

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -The Multiplication Table of: 21 21 x 1 = 21 21 x 2 = 42 21 x 3 = 63 21 x 4 = 84 21 x 5 = 105 21 x 6 = 126 21 x 7 = 147 21 x 8 = 168 21 x 9 = 189 21 x 10 = 210

Python While Loop with List

Program Code 1:

Now we give code examples of while loops in Python for square every number of a list. The code is given below –

# Python program to square every number of a list    

# initializing a list    

list_ = [3, 5, 1, 4, 6]    

squares = []    

# programing a while loop     

while list_: # until list is not empty this expression will give boolean True after that False    

    squares.append( (list_.pop())**2)    

#  Print the squares of all numbers.  

print( squares )

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -[36, 16, 1, 25, 9]

In the preceding example, we execute a while loop over a given list of integers that will repeatedly run if an element in the list is found.

Program Code 2:

Now we give code examples of while loops in Python for determine odd and even number from every number of a list. The code is given below –

list_ = [3, 4, 8, 10, 34, 45, 67,80]        # Initialize the list  

index = 0  

while index < len(list_):  

    element = list_[index]  

    if element % 2 == 0:  

        print('It is an even number')       # Print if the number is even.  

    else:  

        print('It is an odd number')        # Print if the number is odd.  

    index += 1

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -It is an odd number It is an even number It is an even number It is an even number It is an even number It is an odd number It is an odd number It is an even number

Program Code 3:

Now we give code examples of while loops in Python for determine the number letters of every word from the given list. The code is given below –

List_= ['Priya', 'Neha', 'Cow', 'To']  

index = 0  

while index < len(List_):  

    element = List_[index]  

    print(len(element))  

    index += 1

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -5 4 3 2

Python While Loop Multiple Conditions

We must recruit logical operators to combine two or more expressions specifying conditions into a single while loop. This instructs Python on collectively analyzing all the given expressions of conditions.

We can construct a while loop with multiple conditions in this example. We have given two conditions and a and keyword, meaning the Loop will execute the statements until both conditions give Boolean True.

Program Code:

Now we give code examples of while loops in Python for multiple condition. The code is given below –

num1 = 17  

num2 = -12  

   

while num1 > 5 and num2 < -5 : # multiple conditions in a single while loop  

    num1 -= 2  

    num2 += 3  

    print( (num1, num2) )

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -(15, -9) (13, -6) (11, -3)

Let’s look at another example of multiple conditions with an OR operator.

num1 = 17  

num2 = -12  

   

while num1 > 5 or num2 < -5 :  

    num1 -= 2  

    num2 += 3  

    print( (num1, num2) )

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -(15, -9) (13, -6) (11, -3) (9, 0) (7, 3) (5, 6)

We can also group multiple logical expressions in the while loop, as shown in this example.

Code

num1 = 9   

num = 14   

maximum_value = 4  

counter = 0   

while (counter < num1 or counter < num2) and not counter >= maximum_value: # grouping multiple conditions  

    print(f"Number of iterations: {counter}")   

    counter += 1

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -Number of iterations: 0 Number of iterations: 1 Number of iterations: 2 Number of iterations: 3

Single Statement While Loop

Similar to the if statement syntax, if our while clause consists of one statement, it may be written on the same line as the while keyword.

Here is the syntax and example of a one-line while clause –

# Python program to show how to create a single statement while loop  

counter = 1  

while counter: print('Python While Loops')

Loop Control Statements

Now we will discuss the loop control statements in detail. We will see an example of each control statement.

Continue Statement

It returns the control of the Python interpreter to the beginning of the loop.

Code

# Python program to show how to use continue loop control  

  

# Initiating the loop  

for string in "While Loops":  

    if string == "o" or string == "i" or string == "e":  

         continue  

    print('Current Letter:', string)

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below –

Output:Current Letter: W Current Letter: h Current Letter: l Current Letter: Current Letter: L Current Letter: p Current Letter: s

Break Statement

It stops the execution of the loop when the break statement is reached.

Code

# Python program to show how to use the break statement  

  

# Initiating the loop  

for string in "Python Loops":  

    if string == 'n':  

         break  

    print('Current Letter: ', string)

Output:

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below -Current Letter: P Current Letter: y Current Letter: t Current Letter: h Current Letter: o

Pass Statement

Pass statements are used to create empty loops. Pass statement is also employed for classes, functions, and empty control statements.

Code

# Python program to show how to use the pass statement    

for a string in "Python Loops":    

    pass    

print( 'The Last Letter of given string is:', string)

Now we compile the above code in python, and after successful compilation, we run it. Then the output is given below –

Output:The Last Letter of given string is: s