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26. Defensive Programming

Defensive programming is about writing code that anticipates and guards against errors.

Examples of Defensive Programming​

Validate Inputs​

def divide(a, b):
    if b == 0:
        raise ValueError("Denominator cannot be zero")
    return a / b

Use Defaults Carefully​

def add_item(item, container=None):
    if container is None:
        container = []
    container.append(item)
    return container

Fail Fast​

Raise errors early instead of allowing incorrect state to spread.

Practice Challenge​

Write a function safe_average(numbers) that checks the list is not empty before computing the average.

Wrap-Up​

Defensive programming improves reliability by preventing invalid states and handling errors early.