'Returns this course\'s number.
This is a "number" in the sense of the "course numbers" that you see at
lots of universities. For example, given a course
"Intro to Computer Science" with the course key "edX/CS-101/2014", the
course number would be "CS-101"'

@property
def number(self):

    return course_metadata_utils.number_for_course_location(self.location)
