WordPress - get images in current post with short code

functions.php

// Use this in the content of a post or page. 
// [get_images size="thumbnail" num=3] 

// The code below is added to your functions.php
function get_images_func( $atts ) {
    global $post;
    
    $num = $atts["num"];
    $size = $atts["size"];
    $image_html = ""; // Hello World $size";
    
    
	$attachments = get_posts( array("numberposts" => $num, 
									"post_type" => "attachment", 
									"post_parent" => $post->ID, 
									"orderby" => "name" ) );
    
	foreach( $attachments as $attachment ) {
		$img = wp_get_attachment_image( $attachment->ID, $size ); 
		$image_html .= "<div class='post-img grid-20'>$img</div>";
	}
    
    return $image_html;
}

function register_shortcodes(){
   add_shortcode( 'get-images', 'get_images_func' );
}

add_action( 'init', 'register_shortcodes');