Force drop user in Oracle database

gistfile1.sql

DECLARE
  open_count integer;
BEGIN
  -- prevent any further connections
  EXECUTE IMMEDIATE 'alter user @USERNAME account lock';
  --kill all sessions
  FOR session IN (SELECT sid, serial# 
                  FROM  v$session 
                  WHERE username = '@USERNAME')
  LOOP
    -- the most brutal way to kill a session
    EXECUTE IMMEDIATE 'alter system disconnect session ''' || session.sid || ',' || session.serial# || ''' immediate';
  END LOOP;
  -- killing is done in the background, so we need to wait a bit
  LOOP
    SELECT COUNT(*) 
      INTO open_count 
      FROM  v$session WHERE username = '@USERNAME';
    EXIT WHEN open_count = 0;
    dbms_lock.sleep(0.5);
  END LOOP;
  -- finally, it is safe to issue the drop statement
  EXECUTE IMMEDIATE 'drop user @USERNAME cascade';
END;