What Optional[str] means

Question

Accepted Answer

Optional[str] is shorthand for Union[str, None], which means the value is either a str or None - nothing else. In Python 3.10+, you can write this more cleanly as 'str | None' using the new union syntax; both mean the same thing. A common misconception is that Optional means 'has a default value' - it doesn't. It means None is a valid value. You still have to explicitly pass None or a str; the parameter is not automatically optional in the function-call sense.