extending core class not function

Code:
&lt;?php

class MY_Exceptions extends CI_Exceptions {



    function __construct(){

   parent::__construct();

 }



    function log_exception($severity, $message, $filepath, $line)



    {   



        $ci =& get_instance();

        $severity = ( ! isset($ci->levels[$severity])) ? $severity : $ci->levels[$severity];



        log_message('error', 'Severity: '.$severity.'  --&gt; '.$message. ' '.$filepath.' '.$line, TRUE);



        $ci->load->library('email');

        $ci->email->from('[email protected]', 'Server Name');

        $ci->email->to('[email protected]');





        $ci->email->subject('error');

        $ci->email->message('Severity: '.$severity.'  --&gt; '.$message. ' '.$filepath.' '.$line);



        $ci->email->send();

    }



}