Python While Loops: Syntax, Examples & Best Practices

Table of Contents

1. What is while loop?
2. Examples
3. Python Loops Performance Comparison: For vs. While | Which is Faster?
4. Tasks

1. What is while loop?

• A while loop in python is a control flow statement that repeatedly executes a block of code until a specified condition is met.

Syntax:

while condition:
    # code block

Here, condition is a boolean expression that is evaluated before each iteration of the loop. If the condition is True, the code block is executed. The loop continues to execute as long as the condition remains True.

video: Python while loop example - Learn how to use while loop

2. Examples

Example 1: Print numbers from 1 to 10 using while loop

Question: Write a Python program to print the numbers from 1 to 10, using a while loop?

count = 1  # Start counting at 1
while count <= 10:  # Keep counting as long as we're less than or equal to 10
    print(count)  # Print the current number
    count += 1  # Add 1 to the count for the next round

Example 2: Print "Hello, world!" 5 times using while loop

Question: Write a Python program to print the string "Hello, world!" 5 times, using a while loop?

i = 1
while i <= 10:
    print('Hello, world!')
    i += 1

Example 3: Sum of even numbers from 2 to 20 using while loop

Question: Write a Python program to calculate the sum of the even numbers from 2 to 20 using a while loop.

sum = 0  # Initialize a variable to store the sum
number = 1  
 
while number <= 20:
    if number%2 == 0:
      sum += number  # Add the current number to the sum
    number += 1
 
print(f'The sum of even numbers from 1 to 20 is: {sum}')

Example 4: Prompt User for Input Until Blank Line is Entered

Question: Write a Python program to prompt the user to enter lines of text until the user enters a blank line. The program should then display the message "You entered a blank line.".

inputStr = 'Start'
 
while inputStr != "":
  inputStr = input("Enter a line of text:")
 
print('You entered a blank line.')

Example 5: Sum User-Entered Numbers Until Zero is Entered

Question: Write a Python program to add all the numbers entered by the user until the user enters zero. The program should display the sum of the numbers.

sum = 0; # Initialize the sum
 
# Prompt the user to enter a number
number = int(input('Enter a number: ')) # int() Convert string input to integer
 
# While the number entered is not zero, add the number to the sum and prompt the user to enter another number
while number != 0:
    sum += number
    number = int(input('Enter another number: ')) # int() Convert string input to integer
    
# Display the sum of the numbers
print(f'The sum of the numbers is: {sum}')

Example 6: Infinite Loop Printing Messages with Counter

Video: Learn how to use INFINITE while loop

x = 1
while True:
    print("To infinity and beyond! We're getting close, on %d now!" % (x))
    x += 1

3. Python Loops Performance Comparison: For vs. While | Which is Faster?

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4. Tasks

Task 1: Display Multiplication Tables**

Description:

Write a Python program that asks the user to input a number and displays its multiplication table up to 10 using a while loop.

Input:

• The program should prompt the user to enter an integer value.

Output:

• The program should display the multiplication table for the entered number in the following format:

n x 1 = n
n x 2 = 2n
...
n x 10 = 10n

Example:

Input:

Enter a number: 5

Output:

5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50

Requirements:

• Use a while loop to generate and display the multiplication table.

Task 2: Sum Integers from 1 to 100 Using While Loop

Write a Python program that calculates the sum of all integers from 1 to 100. The program should use a while loop to iterate through these integers and accumulate their sum.

Input:

• The program initializes a variable i to 1 and a variable sum to 0.
• The loop continues while i is less than or equal to 100.

Expected Output:

• The program will print the total sum of integers from 1 to 100 in the following format:
  Sum = {sum}

Example Output:

Sum = 5050

Explanation: This code uses a while loop to iterate through the integers from 1 to 100. In each iteration, the current value of i is added to the variable sum, and i is incremented by 1. After the loop completes, the total sum is printed.

Task 3: Calculate Squares of Numbers from 1 to 4 Using While Loop

Write a Python program that calculates and prints the square of the numbers from 1 to 4. The program should use a while loop to iterate through these numbers.

Input:

• The program initializes a variable i to 1 and continues looping while i is less than 5.

Expected Output:

• The program will print the square of each number from 1 to 4 in the following format:
  Square of {i} is {square}

Example Output:

Square of 1 is 1
Square of 2 is 4
Square of 3 is 9
Square of 4 is 16

Explanation: This code uses a while loop to calculate the square of the variable i, which starts at 1 and increments by 1 in each iteration until it reaches 5. The squares of the numbers 1 through 4 are printed during each iteration.

Task 4: Sum User-Entered Numbers Until a Negative Number is Entered

Write a Python program that prompts the user to enter numbers. The program should keep accepting numbers until the user enters a negative number. Once a negative number is entered, the program should stop and display the sum of all the numbers entered (excluding the negative number).

Sample Input:

Enter a number (negative number to stop): 10
Enter another number (negative number to stop): 20
Enter another number (negative number to stop): 5
Enter another number (negative number to stop): -1

Sample Output:

The sum of all numbers is: 35

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