Validation in Python

Lesson overview

Topic

Validation and testing

Level

GCSE

Learning objective

Use a validation loop to keep asking for input until it meets a rule.

1.Predict

Example code

age = 0
while age < 11 or age > 16:
    age = int(input("Enter an age from 11 to 16: "))
print("Age accepted")

• When will the loop stop repeating?
• What do you think happens if someone enters 9 first?

2.Run

Run the code in Paired and test both valid and invalid ages to see how the loop behaves.

3.Investigate

• The loop keeps running while the input is outside the allowed range.
• This is a common validation pattern for classroom programs.

• Why is age given a starting value before the loop begins?
• How do the conditions work together to reject values outside the range?

4.Modify

• Change the accepted range so the program allows ages from 5 to 12.
• Add another message that tells the user when they need to try again.

5.Make

Create a validation loop for a menu choice or a score that only accepts a sensible range.

Extension

Improve the validation so the user also gets a different message for values that are too low and too high.