Class-Based Decorators — Using __call__

"Function-based decorators are stateless by default (nonlocal makes them mutable but awkward). Class-based decorators solve this elegantly: the class instance holds state in regular attributes, and the __call__ method makes the instance callable. This is perfect for things like call counters, rate limiters, circuit breakers, and caches — all stateful decorators that need to remember something between calls. Today you build stateful decorators for the budget dashboard."