How to use the maxminddb.const.MODE_MMAP function in maxminddb

def __init__(self, database, mode=MODE_AUTO):
        """Reader for the MaxMind DB file format

        Arguments:
        database -- A path to a valid MaxMind DB file such as a GeoIP2 database
                    file, or a file descriptor in the case of MODE_FD.
        mode -- mode to open the database with. Valid mode are:
            * MODE_MMAP - read from memory map.
            * MODE_FILE - read database as standard file.
            * MODE_MEMORY - load database into memory.
            * MODE_AUTO - tries MODE_MMAP and then MODE_FILE. Default.
            * MODE_FD - the param passed via database is a file descriptor, not
                        a path. This mode implies MODE_MEMORY.
        """
        if (mode == MODE_AUTO and mmap) or mode == MODE_MMAP:
            with open(database, 'rb') as db_file:
                self._buffer = mmap.mmap(
                    db_file.fileno(), 0, access=mmap.ACCESS_READ)
                self._buffer_size = self._buffer.size()
            filename = database
        elif mode in (MODE_AUTO, MODE_FILE):
            self._buffer = FileBuffer(database)
            self._buffer_size = self._buffer.size()
            filename = database
        elif mode == MODE_MEMORY:
            with open(database, 'rb') as db_file:
                self._buffer = db_file.read()
                self._buffer_size = len(self._buffer)
            filename = database
        elif mode == MODE_FD:
            self._buffer = database.read()

* MODE_MMAP - read from memory map. Pure Python.
            * MODE_FILE - read database as standard file. Pure Python.
            * MODE_MEMORY - load database into memory. Pure Python.
            * MODE_FD - the param passed via database is a file descriptor, not
                        a path. This mode implies MODE_MEMORY.
            * MODE_AUTO - tries MODE_MMAP_EXT, MODE_MMAP, MODE_FILE in that
                          order. Default mode.
    """
    has_extension = maxminddb.extension and hasattr(maxminddb.extension, "Reader")
    if (mode == MODE_AUTO and has_extension) or mode == MODE_MMAP_EXT:
        if not has_extension:
            raise ValueError(
                "MODE_MMAP_EXT requires the maxminddb.extension module to be available"
            )
        return maxminddb.extension.Reader(database)
    if mode in (MODE_AUTO, MODE_MMAP, MODE_FILE, MODE_MEMORY, MODE_FD):
        return PyReader(database, mode)
    raise ValueError("Unsupported open mode: {0}".format(mode))

* MODE_FILE - read database as standard file. Pure Python.
            * MODE_MEMORY - load database into memory. Pure Python.
            * MODE_FD - the param passed via database is a file descriptor, not
                        a path. This mode implies MODE_MEMORY.
            * MODE_AUTO - tries MODE_MMAP_EXT, MODE_MMAP, MODE_FILE in that
                          order. Default mode.
    """
    has_extension = maxminddb.extension and hasattr(maxminddb.extension,
                                                    'Reader')
    if (mode == MODE_AUTO and has_extension) or mode == MODE_MMAP_EXT:
        if not has_extension:
            raise ValueError(
                "MODE_MMAP_EXT requires the maxminddb.extension module to be available"
            )
        return maxminddb.extension.Reader(database)
    elif mode in (MODE_AUTO, MODE_MMAP, MODE_FILE, MODE_MEMORY, MODE_FD):
        return maxminddb.reader.Reader(database, mode)
    raise ValueError('Unsupported open mode: {0}'.format(mode))

def __init__(self, database, mode=MODE_AUTO):
        """Reader for the MaxMind DB file format

        Arguments:
        database -- A path to a valid MaxMind DB file such as a GeoIP2 database
                    file, or a file descriptor in the case of MODE_FD.
        mode -- mode to open the database with. Valid mode are:
            * MODE_MMAP - read from memory map.
            * MODE_FILE - read database as standard file.
            * MODE_MEMORY - load database into memory.
            * MODE_AUTO - tries MODE_MMAP and then MODE_FILE. Default.
            * MODE_FD - the param passed via database is a file descriptor, not
                        a path. This mode implies MODE_MEMORY.
        """
        if (mode == MODE_AUTO and mmap) or mode == MODE_MMAP:
            with open(database, 'rb') as db_file:
                self._buffer = mmap.mmap(db_file.fileno(),
                                         0,
                                         access=mmap.ACCESS_READ)
                self._buffer_size = self._buffer.size()
            filename = database
        elif mode in (MODE_AUTO, MODE_FILE):
            self._buffer = FileBuffer(database)
            self._buffer_size = self._buffer.size()
            filename = database
        elif mode == MODE_MEMORY:
            with open(database, 'rb') as db_file:
                self._buffer = db_file.read()
                self._buffer_size = len(self._buffer)
            filename = database
        elif mode == MODE_FD: