I am new to sqlalchemy and have an issue connecting to the database when trying to run a script from a separate module.

我是新手，在尝试从单独的模块运行脚本时，连接到数据库时遇到问题。

For context I am trying to connect to a database and return the information as a panda. This works fine when I have the whole script in one file. When I have two separate files and import the necessary class, it no longer works and won't connect to the DB.

对于上下文，我正在尝试连接到一个数据库，并以熊猫的形式返回信息。当我将整个脚本放在一个文件中时，这可以很好地工作。当我有两个单独的文件并导入必要的类时，它不再工作，也不会连接到数据库。

Below is the code, which works fine when all in one module. When I take the data_extraction class to a separate module and import the DatabaseConnector class in from the relevant module, it no longer works. There is no connection to the DB.
I get the following error:

下面是代码，当所有模块都在一个模块中时，它工作得很好。当我将DATA_EXTRACTION类放到单独的模块中并从相关模块导入DatabaseConnector类时，它不再起作用。没有连接到数据库。我得到以下错误：

AttributeError ---> 19 df = pd.read_sql_table(table_name, dbconnector.init_db_engine()) AttributeError: 'NoneType' object has no attribute 'cursor'

I really need these classes in separate files, any help welcome.

我真的需要这些类在单独的文件中，欢迎任何帮助。

class DatabaseConnector:

    def read_db_creds(self): #reads db credentials
        with open(r'db_credentials.yml') as file:
        creds = yaml.safe_load(file)
        connection_url = f"postgresql://{creds['RDS_USER']}:  {creds['RDS_PASSWORD']}@{creds['RDS_HOST']}:{creds['RDS_PORT']}/{creds['RDS_DATABASE']}"
    return connection_url


    def init_db_engine(self): # creates engine
        self.engine = db.create_engine(self.read_db_creds())
        return self.engine


class data_extraction(): # extracts data to panda
 
     def read_rds_table(self, dbconnector, table_name):
         df = pd.read_sql_table(table_name, dbconnector.init_db_engine())
         return df.head()

 dc_instance = DatabaseConnector() # an instance of the DatabaseConnector class
 de = data_extraction() # # an instance of the DatabaseConnector class
 de.read_rds_table(dc_instance, 'legacy_store')