While Loop in Python

Welcome back! In the previous tutorial, we learned about the for loop and how it allows us to iterate over sequences. Now, let’s dive into another powerful looping construct: the while loop. The while loop in Python is used to repeatedly execute a block of code as long as a given condition is true. This is especially useful when the number of iterations is not known beforehand. In this article, we’ll explore how to use the while loop in Python effectively.

What is a While Loop?

A while loop repeatedly executes a block of code as long as the specified condition evaluates to True. The condition is checked before each iteration, and if it evaluates to False, the loop terminates.

Syntax

The basic syntax of a while loop in Python is:

while condition:
    # Code to execute while the condition is true

Here, condition is a boolean expression that is evaluated before each iteration. If the condition is True, the code inside the while block is executed. If the condition is False, the loop terminates, and the program continues with the next statement after the loop.

Example: Simple While Loop

Let’s start with a simple example of a while loop that prints numbers from 1 to 5.

count = 1

while count <= 5:
    print(count)
    count += 1

Output:

1
2
3
4
5

In this example, the while loop iterates as long as count is less than or equal to 5. The count variable is incremented by 1 in each iteration.

Infinite Loop

A while loop can become an infinite loop if the condition never evaluates to False. An infinite loop will keep running until you manually interrupt it or force the program to stop.

Example: Infinite Loop

while True:
    print("This is an infinite loop. Press Ctrl+C to stop.")

Be cautious with infinite loops, as they can cause your program to hang.

Using break Statement

The break statement is used to exit a loop prematurely, even if the loop’s condition is still True.

Example: Using break in a While Loop

count = 1

while count <= 10:
    print(count)
    if count == 5:
        break
    count += 1

Output:

1
2
3
4
5

In this example, the while loop is terminated when count equals 5, thanks to the break statement.

Using continue Statement

The continue statement is used to skip the current iteration of the loop and proceed to the next iteration.

Example: Using continue in a While Loop

count = 0

while count < 10:
    count += 1
    if count % 2 == 0:
        continue
    print(count)

Output:

1
3
5
7
9

In this example, the while loop skips the current iteration when count is even, thanks to the continue statement.

Using else with While Loop

The else block can be used with a while loop. The else block is executed when the loop condition becomes False.

Example: Using else with While Loop

count = 1

while count <= 5:
    print(count)
    count += 1
else:
    print("Loop has ended.")

Output:

1
2
3
4
5
Loop has ended.

In this example, the else block is executed after the while loop finishes iterating.

Example: Using While Loop in a Program

Let’s create a simple program that prompts the user to guess a number between 1 and 10.

import random

# Generate a random number between 1 and 10
target_number = random.randint(1, 10)

# Initialize the guess variable
guess = None

# Start the while loop
while guess != target_number:
    guess = int(input("Guess a number between 1 and 10: "))

    if guess < target_number:
        print("Too low! Try again.")
    elif guess > target_number:
        print("Too high! Try again.")

print("Congratulations! You guessed the correct number.")

In this program, we:

1. Generate a random number between 1 and 10 using the random.randint() function.
2. Initialize the guess variable to None.
3. Use a while loop to repeatedly prompt the user to guess the number.
4. Provide feedback if the guess is too low or too high.
5. Congratulate the user when they guess the correct number.

Conclusion

The while loop is a powerful control structure in Python that allows you to execute a block of code repeatedly based on a condition. Understanding how to use while loops, along with the break and continue statements, will help you write more flexible and dynamic programs.

In our next tutorial, we’ll explore functions in Python, which allow you to organize your code into reusable blocks. Stay tuned, and happy coding!