Optional & Union

Many real functions don't return one neat type. A lookup might find a product or come back empty. A field might hold a customer ID or be missing. A parsed value might be an int when the input was numeric and a string otherwise. Python's type system handles all of this with two related constructs: Optional[X] for "X or None", and Union[A, B] for "one of several types". Since Python 3.10 (PEP 604), the | operator collapses both into a shorter syntax. This lesson covers every flavor, how to handle these types safely in code, and the patterns that keep annotations honest.