Raise clear errors for invalid values

Some inputs have the right type but still make no sense for a task. A study duration of zero or less is an example. Type hints do not enforce types at runtime, so check the exact type as well as the range. type(value) is int rejects strings and Boolean values; raise stops the operation with a useful exception.

def positive_minutes(value: int) -> int:
    """Return a positive integer duration or raise ValueError."""
    if type(value) is not int or value <= 0:
        raise ValueError("minutes must be a positive integer")
    return value

print(positive_minutes(25))

25

Handle it at the right boundary

The caller can catch the specific ValueError and show a friendly message. The validation function itself stays focused on checking its rule.

def positive_minutes(value: int) -> int:
    if type(value) is not int or value <= 0:
        raise ValueError("minutes must be a positive integer")
    return value

try:
    positive_minutes(0)
except ValueError as error:
    print(error)

minutes must be a positive integer

Why this works

Parsing and validation answer different questions. int("0") parses successfully because 0 is an integer, but a positive-duration rule rejects it. The exact type check also rejects True, which otherwise behaves like an integer in comparisons. raise ValueError communicates that the value is unsuitable; a caller can catch it.

Practice

Write a function that requires a positive integer session count. Test it with 3, 0, and True, catching the error for the two invalid values at the call site.

Try another case

What happens for positive_minutes(-5) and positive_minutes(True)?