Get excerpt by post id in wordpress

// Function add in function.php

function get_excerpt_by_id($post_id){
   $the_post = get_post($post_id);
   $the_excerpt = $the_post->post_content;
   $excerpt_length = 35;    //Sets excerpt length by word count
   $the_excerpt = strip_tags(strip_shortcodes($the_excerpt));
   $words = explode(' ', $the_excerpt, $excerpt_length + 1);

   if(count($words) > $excerpt_length) :
       array_pop($words);
       array_push($words, '…');
       $the_excerpt = implode(' ', $words);
   endif;

   $the_excerpt = '<p>' . $the_excerpt . '</p>';

   return $the_excerpt;
}

// Call in template files

echo get_excerpt_by_id($post_id);   // you will get excerpt by post id