Python for Data Analytics • Lesson 14

while Loops

Learn how Python repeats code while a condition remains True. Practice counters, validation, output prediction, debugging and data analytics examples.

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Concept 1WHILE

What Is a while Loop?

A while loop repeats a block of code as long as its condition is True. The condition is checked before every iteration, and the loop stops the moment the condition becomes False.

Learn by Seeing

Repeat while True

count = 1

while count <= 5:
    print(count)
    count = count + 1

Python checks the condition first, then runs the body, then checks again.

Adjust n — see how many iterations the while loop runs:

iterations

12345

The loop checks the condition before each run.

Interactive Activity

How many times does the loop body run in the example above (count = 1 to 5)?

Hint: count takes the values 1, 2, 3, 4, 5.

Python Analyst Mindset

Loops that know when to stop

for loops are for fixed sequences. while loops are for anything with a stopping condition — reaching a target, waiting for a valid value, or processing until a business limit is hit. The discipline is always the same: make sure the condition can eventually become False.

Condition

What must stay True?

Update

Change something each pass.

Exit

Confirm a path to False.

Filter

Add if inside for logic.

Frequently Asked Questions

while Loops — FAQs

When should I use while instead of for?

Use for when iterating a known sequence. Use while when the number of iterations depends on a condition (e.g. reaching a target).

Can a while loop run zero times?

Yes. If the condition is False the first time it is checked, the body never runs.

How do I stop an infinite loop?

Fix the logic — ensure the loop variable changes each iteration so the condition eventually becomes False. Ctrl+C stops a running program.

Does while support else?

Yes — while loops can have an else clause that runs when the condition becomes False (unless the loop is exited with break). This is rarely used.

Lesson Summary

What you learned

while

Repeats while the condition is True.

Counters

Start a variable and update it each iteration.

+= 1

Advance the counter in one step.

Infinite loops

Happen when the loop variable never changes.

while + if

Process and filter in the same loop.

Validation

Continue until a business target or valid state is reached.