Raise ValueError exception

You can be more specific with your error type and raise a ValueError.

def add_material(name, amount):
    if amount <= 0:
        raise ValueError(f"Amount of {name} must be positive. {amount} was given.")
    print(f"Adding {name}: {amount}")

def main():
    things_to_add = (
        ("apple", 3),
        ("sugar", -1),
        ("banana", 2),

    for name, amount in things_to_add:
            add_material(name, amount)
        except Exception as err:
            print(f"Exception: {err}")
            print("Type: " + type(err).__name__)


$ python raise_value_error.py
Adding apple: 3
Exception: Amount of sugar must be positive. -1 was given.
Type: ValueError
Adding banana: 2