Block IP via php in wp-config.php

gistfile1.txt

if ( !file_exists('blocked_ips.txt') ) {
 $deny_ips = array(
  '127.0.0.1',
 );
} else {
 $deny_ips = file('blocked_ips.txt');
}
// read user ip adress:
$ip = isset($_SERVER['REMOTE_ADDR']) ? trim($_SERVER['REMOTE_ADDR']) : '';
 
// search current IP in $deny_ips array
if ( (array_search($ip, $deny_ips))!== FALSE ) {
 // address is blocked:
 echo 'Sorrty!';
 exit;
}