Python Practice 6/9

Error handling

raise ValueError("message") stops the function right there and hands the caller a specific, named problem instead of a wrong answer or a crash further down the line. It's how you say "this input is bad, and here's exactly why" - far more useful to whoever calls your function than a silent None or a confusing error somewhere else.

try / except is how the caller decides what to do about it. Code inside try runs normally until something raises; except ValueError: catches that specific exception type and runs its block instead of letting the program crash. Catching the exact exception type matters - an unrelated bug shouldn't get silently swallowed along with the one you meant to handle.

Your task: write divide(a, b), which raises ValueError("cannot divide by zero") when b is 0, and otherwise returns a / b. Then write safe_divide(a, b), which calls divide(a, b) but catches that ValueError and returns None instead of letting it propagate.

You'll practice:

Raising a specific exception with raise
Catching it with try / except and building one function on another

# Write divide(a, b): raise ValueError("cannot divide by zero") when b is 0,
# otherwise return a / b.
def divide(a, b):
    pass

# Write safe_divide(a, b): call divide(a, b), but catch that ValueError
# and return None instead of letting it propagate.
def safe_divide(a, b):
    pass