:param courseid: 
        :return: a FileSystemProvider pointing to the directory of the course

def get_course_fs(self, courseid):
        """
        :param courseid: 
        :return: a FileSystemProvider pointing to the directory of the course 
        """
        if not id_checker(courseid):
            raise InvalidNameException("Course with invalid name: " + courseid)
        return self._filesystem.from_subfolder(courseid)