扭曲延迟模式，用于保护未初始化的数据库

pip install twisted

from twisted.internet import reactor, defer

# 模拟数据库初始化
def initialize_database():
    d = defer.Deferred()
    
    def on_database_initialized():
        print("Database initialized.")
        d.callback("Database connection")
    
    # 模拟异步初始化过程
    reactor.callLater(2, on_database_initialized)
    return d

# 模拟数据库查询
def query_database(connection):
    d = defer.Deferred()
    
    def on_query_completed():
        print("Query completed.")
        d.callback("Query result")
    
    # 模拟异步查询过程
    reactor.callLater(1, on_query_completed)
    return d

def main():
    # 初始化数据库
    db_init_deferred = initialize_database()
    
    def on_database_initialized(connection):
        print("Database is ready. Connection:", connection)
        
        # 在数据库初始化完成后执行查询操作
        query_deferred = query_database(connection)
        
        def on_query_completed(result):
            print("Query result:", result)
            reactor.stop()
        
        query_deferred.addCallback(on_query_completed)
    
    db_init_deferred.addCallback(on_database_initialized)

if __name__ == "__main__":
    main()
    reactor.run()