def METHOD_NAME(self):
    """
    :return: file path from directory path
    :rtype: string
    """
    if not self.file_path.startswith(self.dir_path):
        msg = "Expecting %s to start with %s" % (self.file_path, self.dir_path)
        raise AttributeError(msg)
    return self.file_path.split(self.dir_path)[1].strip("/")