Python While Loop

Python While Loops at a Glance

Iteration means repeating a block of code. A while loop repeats while its condition is True and checks that condition before every iteration.

1. Python While Loop Visual Summary

Use this infographic to review the condition flow, basic syntax, and the different effects of break, continue, and loop else.

2. While Loop

Python provides two common loop options: while loops and for loops. A while loop is useful when you do not know beforehand how many iterations are needed. It keeps running as long as its condition is true.

Here is a basic example:

counter = 0

while counter < 3:
    counter += 1
    print("Counter value is %s" % counter)

The code produces this output:

Counter value is 1
Counter value is 2
Counter value is 3

The condition is checked before each iteration. The loop prints a message and increases counter by 1. Once counter equals 3, counter < 3 is false and execution continues after the loop.

3. Break

The break statement exits the nearest loop immediately, even when the loop condition is still true.

counter = 0

while counter < 3:
    print("Counter value is %s" % counter)
    if counter == 2:
        break
    counter += 1

print("Finished loop")

Counter value is 0
Counter value is 1
Counter value is 2
Finished loop

When counter equals 2, break transfers control to the first statement after the loop. The increment below the if block does not run during that final iteration.

4. Continue Statement

The continue statement stops the current iteration and returns to the next condition check. Code after continue in the same loop body is skipped for that iteration.

counter = 0

while counter < 3:
    counter += 1
    if counter == 2:
        continue
        print("this is never executed")
    print("Counter value is %s" % counter)

Counter value is 1
Counter value is 3

The loop skips the print statement when the value is 2, then continues until the while condition becomes false. In production code, remove statements placed after an unconditional continue because they can never run.

5. Else Statement

A while loop can have an else block. It runs after the condition becomes false and the loop finishes normally.

counter = 0

while counter < 3:
    counter += 1
    print("Counter value is %s" % counter)
else:
    print("We completed increasing the counter")

Counter value is 1
Counter value is 2
Counter value is 3
We completed increasing the counter

The final message appears because the condition became false normally. If a break statement exits the loop, the else block is skipped. This makes else useful for code that should run only when a search or retry loop completes without an early exit.

6. Network Automation Example

A bounded while loop can model a retry workflow. This safe example reads simulated interface states rather than contacting a device:

states = ["down", "down", "up"]
attempt = 0

while attempt < len(states):
    state = states[attempt]
    attempt += 1
    print(f"Attempt {attempt}: interface is {state}")

    if state == "up":
        print("Interface is ready")
        break
else:
    print("Interface did not become ready")

Attempt 1: interface is down
Attempt 2: interface is down
Attempt 3: interface is up
Interface is ready

The counter limits the number of checks, and break exits when the desired state appears. A real polling script should also use a delay, a timeout, exception handling, and read-only device access. Never create a fast, unlimited loop that repeatedly contacts production equipment.

7. Guided Practice

8. Conclusion

You learned how Python controls repetition with a while loop:

• A while loop keeps iterating until its condition becomes false.
• break stops the loop even when the condition is still true.
• continue skips the rest of the current iteration and begins the next condition check.
• The loop else block runs after normal completion, but not after break.

Use explicit counters, limits, and exit conditions so every automation loop has a predictable stopping point.