def METHOD_NAME(self):
    """Return a list of files opened by the project."""
    # Check if recent_files in [main] (Spyder 4)
    recent_files = self.get_option("recent_files", 'main', [])
    if recent_files:
        # Move to [workspace] (Spyder 5)
        self.config.remove_option('main', 'recent_files')
        self.set_recent_files(recent_files)
    else:
        recent_files = self.get_option("recent_files", default=[])
    recent_files = [recent_file if osp.isabs(recent_file)
                    else osp.join(self.root_path, recent_file)
                    for recent_file in recent_files]
    for recent_file in recent_files[:]:
        if not osp.isfile(recent_file):
            recent_files.remove(recent_file)
    return list(OrderedDict.fromkeys(recent_files))