安全取消订阅可选控制器订阅

class SubscriptionService:
    def __init__(self):
        self.subscriptions = {}

    def subscribe(self, user_id, service_name):
        if user_id not in self.subscriptions:
            self.subscriptions[user_id] = []
        self.subscriptions[user_id].append(service_name)
        print(f"User {user_id} subscribed to {service_name}")

    def unsubscribe(self, user_id, service_name):
        if user_id in self.subscriptions and service_name in self.subscriptions[user_id]:
            self.subscriptions[user_id].remove(service_name)
            print(f"User {user_id} unsubscribed from {service_name}")
        else:
            print(f"User {user_id} is not subscribed to {service_name}")

# 示例使用
subscription_service = SubscriptionService()
subscription_service.subscribe("user1", "serviceA")
subscription_service.unsubscribe("user1", "serviceA")