def write(self):
        """ Writes all tensors to the next file number. """
        # write the next file for all fields
        for field_name in self.field_names:
            filename = self.generate_tensor_filename(field_name, self._num_tensors-1)
            self._tensors[field_name].save(filename, compressed=True)

        # write the current metadata to file
        json.dump(self._metadata, open(self.metadata_filename, 'w'),
                  indent=JSON_INDENT,
                  sort_keys=True)

        # update
        self._has_unsaved_data = False
Writes all tensors to the next file number.