Python While Loop is used to repeatedly execute a block of code as long as a given condition remains True. It is useful when the number of iterations is unknown beforehand. The While loop can be utilized by using the while keyword and a colon(:).
In the Python while loop, there can be a single statement or multiple statements with proper indentation. The While enables the program to run till the given condition is True; it stops as soon as the condition fails. If the condition doesn’t fail, the program goes into an infinite loop and doesn’t stop unless forced.
Syntax of the while Loop
Let’s see the basic syntax of the While loop in Python:
while condition:
# The Code to be executed as long as the condition remains trueSyntax Explanation:
The Python While loop evaluates the specified conditional expression. The while loop executes the program if the given condition turns out to be True. When the entire code block is executed, the condition is checked again, and this process is repeated until the conditional expression returns False.
Simple Python while Loop Example:
Let us take a look at a simple example of a Python while loop.
# initializing a counter variable
counter = 0
# using the while loop to iterate the counter up to 5
while counter < 5:
# printing the counter value and some statement
print(counter, "Hello")
# incrementing the counter value
counter += 1Output:
0 Hello
1 Hello
2 Hello
3 Hello
4 Hello
Explanation:
In the above example, we have initialized a variable counter with the value 0. We then enter a while loop that executes the block of code as long as the counter is less than 5. Within the loop, we have printed the current value of the counter, followed by “Hello”. After each iteration, the counter is incremented by 1. Once the counter reaches 5, the condition counter < 5 becomes False, causing the loop to terminate.
Flowchart of the While Loop in Python
The following flowchart represents the working of a ‘while’ loop:
Step 1: The program starts.
Step 2: The while loop checks whether the specified conditional expression is True or False.
- If True, it proceeds to the loop body.
- If False, it exits the loop and moves to the next part of the program.
Step 3: If the condition is True, execute the statements inside the loop.
Step 4: Modify the variable controlling the loop (e.g., incrementing a counter).
Step 5: Go back to Step 2 and re-evaluate the condition.
Step 6: Once the condition becomes False, it exits the loop and continues with the rest of the program.
Note: Indentation is required to define the code block inside a while loop. Improper or Incorrect indentation can cause syntax errors or logical errors (like infinite loops). Any non-zero number in Python is interpreted as Boolean True. False is interpreted as None and 0.
Examples of Python while Loop
We will now take a look at some basic examples of the while loop in Python.
Finding Numbers Divisible by 5 or 7 Using a while Loop
Here, an example is given that elaborates on how to find numbers between 1 and 50 that are divisible by 5 or 7 using the while loop in Python.
Example:
# initializing a iterable as 1
i = 1
# using the while loop to find numbers between 1 to 50 that are divisible by 5 or 7
while i < 50:
if i % 5 == 0 or i % 7 == 0:
print(i, end=' ')
i += 1 Output:
5 7 10 14 15 20 21 25 28 30 35 40 42 45 49Explanation:
In the above example, we are finding the numbers that are divisible by 5 and 7 till the numbers in the loop are less than 50. We start from the initial number 1 and increment it. As soon as the number 50 is reached, the loop gets terminated.
Finding the Sum of Squares Using a While Loop
In the following example, we will show how to calculate the sum of squares of the first 15 natural numbers using the while loop in Python.
Example
# initializing variables
sum = 0 # storing the sum of squares
counter = 1 # iterable
# using the while loop
while counter <= 15:
sum = counter**2 + sum # calculating the sum of the squares
counter += 1 # incrementing the counter value
# printing the result
print("The sum of squares is", sum) Output:
The sum of squares is 1240Explanation:
The above code calculates the sum of squares using a while loop from the numbers 1 to 15. We initialized the variable values of Sum equal to 0 and counter equal to 1. The while loop continues to run as long as the counter value remains less than or equal to 15. The program terminates when the while loop moves ahead to 16 as the condition fails there.
Checking Prime Number using While Loop
In the following example, we will show how to check whether a given number is Prime using while loop in Python.
Example
# creating a list of numbers
num = [34, 12, 54, 23, 75, 34, 11]
# defining a function to check prime number
def prime-number(number):
c = 0
i = 2
while i <= number / 2:
if number % i == 0:
c = 1
break
i = i + 1
if c == 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:
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
Explanation:
In the above example, we are checking whether the numbers in the list are Prime numbers or not. We initialized the value of c, which is equal to 0, and I equals 2. Using the conditions under the while loop and break statement to find out the prime numbers.
Checking Armstrong Number Using while Loop
In the following example, we will show how to check if the given integer is an Armstrong number using the while loop in Python.
An Armstrong number is the sum of each digit raised to the power of the total number of digits. For example: 153 = 1^3 + 5^3 + 3^3 à 1+125+27 = 153
Example
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:
It is an Armstrong numberExplanation:
The above code checks whether a given number is an Armstrong number or not. Initially, we take the input from the user and store it in the variable n. Then the number is converted into a string to calculate its length. We use temp to store the value of the number entered by the users. We initialized the variable s to 0, which will store the sum of powers of digits.
The last digit of the number is found using the modulus operator and stored in r using the while loop. After the loop ends, the program compares the calculated sum s with the original number temp. If both are equal, it prints “It is an Armstrong number”; otherwise, it prints “It is not an Armstrong number”.
Creating Table of Multiplication Using the While Loop
In this example, we will show how to create a multiplication table for a given number using the while loop in Python.
Example
num = 21
counter = 1
# We will use a while loop to iterate 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:
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
Explanation:
In the above example, we are creating a multiplication table of a pre-defined number, 21. We initialized the counter value to 1 and incremented it as the while loop runs. The while loop will function till the counter is less than or equal to 10. These incremented numbers till 10 are multiplied by 21, giving us the multiplication table.
Infinite while Loop in Python
An infinite while loop in Python is caused when the condition always remains true. This causes the loop to run endlessly until the memory gets full.
Let’s see an example where the while loop runs infinitely:
age = 28
# the test condition is always True
while age > 19:
print('Infinite Loop') Output:
Infinite Loop
Infinite Loop
Infinite Loop
Infinite Loop
Infinite Loop
Infinite Loop
Infinite Loop
...... and it continues
Explanation:
In the above example, we created a condition in the while loop that keeps the program in a loop till the age is greater than 19 and assigned the value of the age to 28. As we know that 28 always remains greater than 19, so this condition remains True, which creates an infinite loop. We can exit this infinite loop by forcefully stopping the program or when the memory becomes full.
Loop Control Statements with Python while Loop
Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed. Python supports the following control statements.
We will now look at various loop control statements used in Python’s while loop.
1. Break Statement
The break statement immediately terminates the while loop, regardless of the condition.
Example
i = 0
while i < 8:
if i == 4:
print("Breaking the loop at", i)
break # Exits the loop when i is 4
print("Counter is:", i)
i += 1 Output:
Counter is: 0
Counter is: 1
Counter is: 2
Counter is: 3
Breaking the loop at 4
Explanation:
In the above example, the loop stops as soon as the counter reaches 4, even though the original condition was counter < 8.
2. continue Statement
The continue statement skips the current iteration and moves to the next one without executing the remaining code inside the loop.
Example
i = 0
while i < 8:
i += 1
if i == 4:
continue # Skip iteration when i is 4
print("Counter is:", i) Output:
Counter is: 1
Counter is: 2
Counter is: 3
Counter is: 5
Counter is: 6
Counter is: 7
Counter is: 8
Explanation:
In the above example, the loop skips the print statement when the counter value is 4; however, it continues executing afterward.
3. Pass Statement
The pass Statement acts as a null operator or placeholder. It is applied when a statement is required syntactically, which means that the statement will be visible in the code but will be ignored; hence, it returns nothing.
Example
i = 0
while i < 8:
if i == 4:
pass # Placeholder for future logic
print("Counter is:", i)
i += 1 Output:
Counter is: 0
Counter is: 1
Counter is: 2
Counter is: 3
Counter is: 4
Counter is: 5
Counter is: 6
Counter is: 7
Explanation:
In this example, the pass statement ensures that Python does not throw an error while we develop the code. Since this function is empty and returns nothing due to the pass statement, there will be no output when we call this function.
4. Else with a while Loop
The else block executes after the loop finishes normally (without a break statement).
Example
#initializing value of counter to 0
counter = 0
#using the while loop to iterate the counter up to 7
while counter <= 7:
print("Counter is:", counter)
counter += 1
#using the else
else:
print("Loop completed successfully!") Output:
Counter is: 0
Counter is: 1
Counter is: 2
Counter is: 3
Counter is: 4
Counter is: 5
Counter is: 6
Counter is: 7
Loop completed successfully!
5. Break statement with Else-while Loop
The Break statement with the else-while loop terminates the program at that very instance when it is executed. In this case, the loop terminates immediately, and the else block is skipped.
Example
i = 0
while i < 8:
print("Counter is:", i)
if i == 4:
break # Loop exits early
i += 1
else:
print("Loop completed successfully!") # This won't execute Output:
Counter is: 0
Counter is: 1
Counter is: 2
Counter is: 3
Counter is: 4
Explanation:
In this example, the else block does not execute as the break statement stops the loop early.
Advantages of the while Loop in Python
There are several advantages of the while loop in Python. Some of them are as follows:
1. Easily Executable
A while loop is one of the best loops in conditions when the number of iterations is unknown, since it runs as long as the condition is True.
2. An effective loop for User Input Programs
It is helpful when the loop’s duration is provided by user input.
3. Prevents Code Duplication
By handling several iterations quickly, a while loop avoids the need to write repeated code and makes the code easier to understand and maintain.
4. Allow Infinite Loops
Infinite loops using True can be helpful in applications like servers, real-time monitoring, and background processes if correctly managed.
5. Conditional Logic
The loop can be readily combined with logical conditions to control program flow because it operates on a condition dynamically.
Disadvantages of While Loop in Python
There are several disadvantages of while loop in Python. Some of them are as follows:
1. Risk of Infinite Loops
The program might get into an endless loop that results in freezing or overuse of the CPU if the loop condition never turns False.
2. Condition Handling Must Be Done by Hand
A while loop needs manual condition management, and there is the possibility of raising errors.
3. Less Readable
Loops can occasionally be more difficult to read and debug than other loops, particularly when complicated conditions are included.
4. Overhead in Performance
When compared to more structured loops, loops might slow down performance by causing unnecessary iterations if they are not appropriately optimized.
If not done carefully, using break and continue instructions inside while loops can make the code more difficult to read and debug.
Conclusion
In the conclusion, Python’s While Loop is used to repeatedly execute a block of code as long as a given condition remains True. It is useful when the number of iterations is unknown beforehand. The While loop can be utilized by using the while keyword and a colon(:).
