code: def parse_course_key(course_identifier):
      
      try:
          course_run_key = CourseKey.from_string(course_identifier)
      except InvalidKeyError:
          # Assume we already have a course key.
          return course_identifier
  
      return quote_plus(' '.join([course_run_key.org, course_run_key.course]))
docs: Return the serialized course key given either a course run ID or course key.