'Check whether the :attr:`database` file exists or not.
.. note:: This is a `classmethod`.
:param database: Path to a SQLite database file.
`./hostslist.s3db` by default.
:type database: str
:return: A flag indicating whether the database file exists or not.
:rtype: bool'

@classmethod
def db_exists(cls, database=DATABASE):

    return os.path.isfile(database)
