在python中打开新数据库之前检查是否存在与数据库的连接

import dataset

class db(object):
    _db_connection = None
    _db_cur = None

    def __init__(self):
        self._db_connection = dataset.connect(path_to_database)

    def __del__(self):
        self._db_connection.executable.close()
import dataset

class db(object):
    _db_conne