def get_course_duration(self, obj):
duration = obj.end - obj.start if obj.start and obj.end else None<EOL>if duration:<EOL><INDENT>return strfdelta(duration, '<STR_LIT>')<EOL><DEDENT>return '<STR_LIT>'<EOL>
Get course's duration as a timedelta.

Arguments:
    obj (CourseOverview): CourseOverview object

Returns:
    (timedelta): Duration of a course.