Introduction to Python While Loop

Python’s while loop is a fundamental part of programming, allowing for repetitive execution of a block of code as long as a specified condition remains true. This guide explains how while loops work, various practical use cases, and how to avoid pitfalls such as infinite loops.

Syntax of Python While Loop

while condition:
    # block of code to be executed
    statement(s)
    

The while keyword begins the loop, followed by a condition. As long as the condition is true, the indented code block runs repeatedly.

Example 1: Basic While Loop

count = 0
while count < 5:
    count += 1
    print("Iteration no. {}".format(count))

print("End of while loop")
    

In this example, the while loop will run until the count variable reaches 5. The loop prints the iteration number each time the block executes.

Output:
Iteration no. 1
Iteration no. 2
Iteration no. 3
Iteration no. 4
Iteration no. 5
End of while loop

Example 2: While Loop with User Input

var = '0'
while var.isnumeric():
    var = input("Enter a number..")
    if var.isnumeric():
        print("Your input: {}".format(var))

print("End of while loop")
    

This example demonstrates a while loop that continues to ask for user input until the input is no longer numeric.

Output:
Enter a number.. 10
Your input: 10
Enter a number.. abc
End of while loop

Handling Infinite Loops

A common issue in using while loops is creating an infinite loop—a loop that runs forever because the condition never becomes false. This is usually unintended, but in some cases, like server-client models, infinite loops can be useful.

var = 1
while var == 1:
    num = int(input("Enter a number: "))
    print("You entered:", num)
print("Goodbye!")
    

If you run the above code, it will continue to ask for a number indefinitely. You can terminate the loop using CTRL + C.