Question 1

What Optional[str] means

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.

Question 2

Basic function annotation syntax

Accepted Answer

Type annotations on parameters and return values are purely informational - Python ignores them at runtime. The function runs exactly as if the annotations weren't there: 2 + 3 = 5. The annotation 'x: int' does not prevent you from passing a string, and '-> int' does not coerce the return value. Annotations are metadata; only external tools like mypy or pyright act on them.

Question 3

Type hints are not enforced at runtime

Accepted Answer

Python does not enforce type hints at runtime - they are annotations only. Passing the string 'ha' where an int is annotated raises no error because Python never checks the annotation. The expression 'ha' * 2 is perfectly valid Python (string repetition), so it prints 'haha'. This is the key fact about type hints: they exist for tools and humans, not for the interpreter. If you want runtime validation, you need a library like Pydantic or explicit isinstance checks.