Validation subprograms

301.16 Defensive Design

Defensive Design — Note 4 of 5

Reusable validation routines.

What you need to know

Writing validation as a function makes it reusable. A validation function takes input, checks it, and either returns the valid value or keeps asking until it's correct.

What to know

Put validation logic in a function for reuse
Function can loop until valid input is received
Return the validated value to the caller
Can be called from anywhere in the program

Code examples

Validation function

python

def get_int_in_range(prompt, low, high):
    value = int(input(prompt))
    while value < low or value > high:
        print("Must be " + str(low) + "-" + str(high))
        value = int(input(prompt))
    return value

age = get_int_in_range("Age: ", 0, 120)

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Specification notes for programming are in Paper 2.