Python while loop

The while loop in Python is used to execute a block of code repeatedly as long as a specified condition is True. It is useful for situations where the number of iterations is not known beforehand and depends on a condition.

Example 

counter = 1

while counter <= 5:

    print(f"Counter: {counter}")

    counter += 1

Output:

Counter: 1

Counter: 2

Counter: 3

Counter: 4

Counter: 5

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Syntax

while condition:

    # Code to execute repeatedly

• condition: A Boolean expression that determines whether the loop should continue. If True, the loop executes; if False, the loop terminates.

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Why Use while?

1. Indeterminate Iterations: Use while when the number of iterations is not fixed and depends on a condition.
2. Event-Driven Loops: For tasks like waiting for user input, monitoring states, or reading files until EOF.
3. Flexible Logic: Can be used with complex conditions for dynamic looping.

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Common Examples

1. Basic While Loop

x = 0

while x < 5:

    print(x)

    x += 1

Output:

0

1

2

3

4

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2. Using a Break Statement

x = 1

while True:

    print(x)

    if x == 5:

        break  # Exit the loop when x reaches 5

    x += 1

Output:

1

2

3

4

5

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3. Using a Continue Statement

x = 0

while x < 5:

    x += 1

    if x == 3:

        continue  # Skip the rest of the loop for x == 3

    print(x)

Output:

1

2

4

5

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4. Validating User Input

while True:

    name = input("Enter your name: ")

    if name.strip():

        print(f"Hello, {name}!")

        break  # Exit loop if input is valid

Input/Output:

Enter your name:

Enter your name: John

Hello, John!

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5. Calculating a Sum

numbers = [1, 2, 3, 4, 5]

total = 0

i = 0

while i < len(numbers):

    total += numbers[i]

    i += 1

print(f"Sum: {total}")

Output:

Sum: 15