Scaffold for db helper

db_helper.py

class DbWorker:
    """Doing the hard work on the DB."""
    def __init__(self, queries):
        self.queries = queries  # old tables

    def _connect(self, credentials):
        # TODO here only db connection stuff - must return the cursor
        # TODO must thrown an exception in error cases
        pass

    def _select_and_insert():
        # TODO use self.cursor
        pass

    def do(self):
        self.cursor = self._connect()
        self._select_and_insert()