WP taxonomy metabox callback to generate radio selection

wp-taxonomy-meta-box-cb.php

<?php
/**
 * Override the default taxonomy metabox
 *
 * Generate a taxonomy meta box with radio button
 */
function op_taxonomy_meta_box_cb( $post ) {
	$_writers         = get_the_terms( $post->ID, 'writer' );
	$selected_writers = array();
	if ( ! empty( $_writers ) || ! is_wp_error( $_writers ) ) {
		foreach ( $_writers as $_writer ) {
			array_push( $selected_writers, $_writer->term_id );
		}
	}

	$writers = get_terms( array(
		'taxonomy' => 'writer',
		'hide_empty' => false
	) );

	echo '<ul class="categorychecklist form-no-clear">';
	if ( ! empty( $writers ) || ! is_wp_error( $writers ) ) {
		foreach ( $writers as $writer ) {
			$selected = false;
			if ( in_array( $writer->term_id, $selected_writers ) ) {
				$selected = true;
			}
			printf( '<li><label><input type="radio" name="tax_input[writer][]" value="%1$s" %3$s>%2$s</label></li>',
				$writer->term_id,
				$writer->name,
				$selected ? 'checked="checked"' : ''
			);
		}
	}
	echo '</ul>';
}