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PYTHON FUNCTIONS / CHAPTER 04 / Learn / LESSON 05

Input Validation.

About 5–10 minutes

Fifth class. Before you compute, check the inputs. If they are invalid — return early. Still no try/except.

def safe_bmi(weight, height):
    if weight <= 0 or height <= 0:
        return None
    return weight / height ** 2

None here means “no valid result”. The caller can check and react.

Common mistake: dividing without a check and hitting ZeroDivisionError; or continuing with negative values “because the formula still runs”.

Your lesson

Write safe_bmi(weight, height): if weight <= 0 or height <= 0 return None, else weight / height ** 2. Print safe_bmi(75, 1.8) and safe_bmi(75, 0). Expected: about 23.15 and None.

Learn: check with if and early return — still no try.

lesson_05.pyPYTHON

Loading the runtime… The first launch may take a little longer.

… 0/20000

STANDBY

input.logIDLE

> waiting for age / height / weight…
> int()/float() idle
> values: —
▌

Code Lab

AWAITING TYPES

01early return on bad input

02valid BMI is about 23.15

03console shows None

ConsoleWrite the code. Bring it online.

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