While Loops

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Python Loops: Mastering the While Loop

In Python, loops are a fundamental part of programming, allowing you to execute a block of code repeatedly. Python offers two basic loop structures:

  • while loops
  • for loops

The While Loop Explained

The while loop in Python enables you to run a set of statements as long as a specified condition remains true. This loop is particularly useful when the number of iterations is not predetermined.

Example: Simple While Loop

Let’s consider an example where we print the value of a variable i as long as it’s less than 6:

i = 1
while i < 6:
    print(i)
    i += 1

In this example, the loop will continue to print the value of i until i is no longer less than 6. It’s important to remember to increment i within the loop; otherwise, you might end up in an infinite loop.

The Importance of Initializing Variables

For a while loop to work correctly, any variables involved in the condition must be initialized beforehand. In the previous example, i is initialized to 1 before the loop starts.

Controlling Loop Execution

Python provides several statements to control the flow of loops, allowing for more complex operations.

The break Statement

The break statement is used to exit the loop prematurely, even if the loop’s condition is still true. This is useful when you need to stop the loop under certain conditions.

Example: Breaking a Loop

Here’s how you can use break to exit a loop when i equals 3:

i = 1
while i < 6:
    print(i)
    if i == 3:
        break
    i += 1

In this scenario, the loop will stop as soon as i equals 3, even though the loop’s condition (i < 6) is still true.

The continue Statement

The continue statement allows you to skip the current iteration of the loop and proceed with the next iteration. This is particularly useful when you need to skip certain values but still continue looping.

Example: Skipping an Iteration

Let’s see an example where the loop skips printing i when i equals 3:

i = 0
while i < 6:
    i += 1
    if i == 3:
        continue
    print(i)

In this case, when i is 3, the loop skips printing it and continues with the next iteration.

The else Statement in Loops

In Python, you can attach an else statement to a while loop. The code block inside the else statement will execute once when the loop condition becomes false.

Example: Using else with a While Loop

Consider the following example where a message is printed once the loop condition is no longer true:

i = 1
while i < 6:
    print(i)
    i += 1
else:
    print("i is no longer less than 6")

Here, after the loop finishes running, the else block executes, printing that i is no longer less than 6.

Test Your Knowledge with Exercises

Ready to put your understanding to the test? Try the following exercise:

Exercise:

Print i as long as i is less than 6.

i = 1
while i < 6:
    print(i)
    i += 1

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