Python while Loops

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Python while Loops

Loops in Python

Loops allow you to execute a block of code repeatedly. Python provides two primary looping constructs:

• while loop – repeats as long as a condition remains true
• for loop – iterates over a sequence (like a list, range, or string)

This section focuses on the while loop.

The while Loop

A while loop runs a block of code as long as a specified condition evaluates to True.

Syntax:

while condition:
    # code to execute

Example: Counting Numbers

count = 0 while count < 5: print("Count value:", count) count += 1

Count value: 0 Count value: 1 Count value: 2 Count value: 3 Count value: 4

• The loop runs while count < 5
• count += 1 is essential to avoid an infinite loop

Note: Always update the condition variable inside the loop.

Preparing the Loop Variable

Before a while loop starts, the variable used in the condition must be initialized.

attempts = 1 while attempts <= 3: print("Attempt number", attempts) attempts += 1

Attempt number 1 Attempt number 2 Attempt number 3

Without initializing attempts, Python would raise an error.

The break Statement

The break statement terminates the loop immediately, even if the condition is still true.

Example: Stop When a Match Is Found

number = 1 while number <= 10: if number == 6: print("Number found, exiting loop") break print(number) number += 1

1 2 3 4 5 Number found, exiting loop

• Loop stops as soon as number becomes 6
• Remaining iterations are skipped

The continue Statement

The continue statement skips the current iteration and moves directly to the next one.

Example: Skip a Specific Value

value = 0 while value < 7: value += 1 if value == 4: continue print("Current value:", value)

Current value: 1 Current value: 2 Current value: 3 Current value: 5 Current value: 6 Current value: 7

• When value is 4, printing is skipped
• Loop continues normally afterward

The else Block in a while Loop

The else block executes once, when the loop condition becomes false naturally (not via break).

Example: Loop Completion Message

steps = 1 while steps <= 3: print("Step", steps) steps += 1 else: print("All steps completed successfully")

Step 1 Step 2 Step 3 All steps completed successfully

• The else block runs after the loop finishes
• Useful for success messages or cleanup tasks

Important Note About break

If a while loop is terminated using break, the else block will not execute.

x = 1 while x <= 5: if x == 3: break print(x) x += 1 else: print("Loop finished")

1 2

Note: "Loop finished" is not printed because the loop exited early.

Common Use Cases of while Loops

• Repeating tasks until user input is valid
• Running background checks
• Implementing retry mechanisms
• Reading data until a condition is met

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