How to use the maxminddb.decoder.Decoder function in maxminddb

'Is this a valid MaxMind DB file?'
                                       ''.format(filename))

        metadata_start += len(self._METADATA_START_MARKER)
        metadata_decoder = Decoder(self._buffer, metadata_start)
        (metadata, _) = metadata_decoder.decode(metadata_start)
        self._metadata = Metadata(**metadata)  # pylint: disable=bad-option-value

        self._ip_version = self._metadata.ip_version
        self._node_byte_size = self._metadata.node_byte_size
        self._node_count = self._metadata.node_count
        self._record_size = self._metadata.record_size

        self._data_pointer_offset = self._metadata.search_tree_size - self._node_count

        self._decoder = Decoder(
            self._buffer, self._metadata.search_tree_size +
            self._DATA_SECTION_SEPARATOR_SIZE)
        self.closed = False

'Unsupported open mode ({0}). Only MODE_AUTO, MODE_FILE, '
                'MODE_MEMORY and MODE_FD are supported by the pure Python '
                'Reader'.format(mode))

        metadata_start = self._buffer.rfind(
            self._METADATA_START_MARKER, max(0,
                                             self._buffer_size - 128 * 1024))

        if metadata_start == -1:
            self.close()
            raise InvalidDatabaseError('Error opening database file ({0}). '
                                       'Is this a valid MaxMind DB file?'
                                       ''.format(filename))

        metadata_start += len(self._METADATA_START_MARKER)
        metadata_decoder = Decoder(self._buffer, metadata_start)
        (metadata, _) = metadata_decoder.decode(metadata_start)
        self._metadata = Metadata(**metadata)  # pylint: disable=bad-option-value

        self._decoder = Decoder(self._buffer, self._metadata.search_tree_size +
                                self._DATA_SECTION_SEPARATOR_SIZE)
        self.closed = False

metadata_start = self._buffer.rfind(
            self._METADATA_START_MARKER, max(0,
                                             self._buffer_size - 128 * 1024))

        if metadata_start == -1:
            self.close()
            raise InvalidDatabaseError('Error opening database file ({0}). '
                                       'Is this a valid MaxMind DB file?'
                                       ''.format(filename))

        metadata_start += len(self._METADATA_START_MARKER)
        metadata_decoder = Decoder(self._buffer, metadata_start)
        (metadata, _) = metadata_decoder.decode(metadata_start)
        self._metadata = Metadata(**metadata)  # pylint: disable=bad-option-value

        self._decoder = Decoder(self._buffer, self._metadata.search_tree_size +
                                self._DATA_SECTION_SEPARATOR_SIZE)
        self.closed = False

'Unsupported open mode ({0}). Only MODE_AUTO, MODE_FILE, '
                'MODE_MEMORY and MODE_FD are supported by the pure Python '
                'Reader'.format(mode))

        metadata_start = self._buffer.rfind(
            self._METADATA_START_MARKER, max(0,
                                             self._buffer_size - 128 * 1024))

        if metadata_start == -1:
            self.close()
            raise InvalidDatabaseError('Error opening database file ({0}). '
                                       'Is this a valid MaxMind DB file?'
                                       ''.format(filename))

        metadata_start += len(self._METADATA_START_MARKER)
        metadata_decoder = Decoder(self._buffer, metadata_start)
        (metadata, _) = metadata_decoder.decode(metadata_start)
        self._metadata = Metadata(**metadata)  # pylint: disable=bad-option-value

        self._ip_version = self._metadata.ip_version
        self._node_byte_size = self._metadata.node_byte_size
        self._node_count = self._metadata.node_count
        self._record_size = self._metadata.record_size

        self._data_pointer_offset = self._metadata.search_tree_size - self._node_count

        self._decoder = Decoder(
            self._buffer, self._metadata.search_tree_size +
            self._DATA_SECTION_SEPARATOR_SIZE)
        self.closed = False