from abc import ABC, abstractmethod

class Handler(ABC):
    def __init__(self, successor=None): self.successor = successor  # Следующий обработчик в цепи
    @abstractmethod
    def handle_request(self, request): pass

class ConcreteHandlerA(Handler):
    def handle_request(self, request):
        if request == "A":
            return f"Handler A handled the request: {request}"
        elif self.successor:
            return self.successor.handle_request(request)
        return "Request not handled"

class ConcreteHandlerB(Handler):
    def handle_request(self, request):
        if request == "B":
            return f"Handler B handled the request: {request}"
        elif self.successor:
            return self.successor.handle_request(request)
        return "Request not handled"

class ConcreteHandlerC(Handler):
    def handle_request(self, request):
        if request == "C": return f"Handler C handled the request: {request}"
        elif self.successor: return self.successor.handle_request(request)
        return "Request not handled"

handler_chain = ConcreteHandlerA(ConcreteHandlerB(ConcreteHandlerC())) # Цепочка обработчиков
requests = ["A", "B", "C", "D"] # Примеры запросов
for req in requests: print(handler_chain.handle_request(req))