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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def connect(self, database_path, mode="a"):
 """ Connect to a SQLite database. :param str database_path: Path to the SQLite database file to be connected. :param str mode: ``"r"``: Open for read only. ``"w"``: Open for read/write. Delete existing tables when connecting. ``"a"``: Open for read/write. Append to the existing tables. :raises ValueError: If ``database_path`` is invalid or |attr_mode| is invalid. :raises simplesqlite.DatabaseError: If the file is encrypted or is not a database. :raises simplesqlite.OperationalError: If unable to open the database file. """


        self.close()

        logger.debug("connect to a SQLite database: path='{}', mode={}".format(database_path, mode))

        if mode == "r":
            self.__verify_db_file_existence(database_path)
        elif mode in ["w", "a"]:
            self.__validate_db_path(database_path)
        else:
            raise ValueError("unknown connection mode: " + mode)

        if database_path == MEMORY_DB_NAME:
            self.__database_path = database_path
        else:
            self.__database_path = os.path.realpath(database_path)

        try:
            self.__connection = sqlite3.connect(database_path)
        except sqlite3.OperationalError as e:
            raise OperationalError(e)

        self.__mode = mode

        try:
            # validate connection after connect
            self.fetch_table_names()
        except sqlite3.DatabaseError as e:
            raise DatabaseError(e)

        if mode != "w":
            return

        for table in self.fetch_table_names():
            self.drop_table(table)