code: def create_variables(self, courses):
          
          has_sections = isinstance(courses, dict)
          for course in courses:
              self.p.add_variable(course, courses.get(course, []) if has_sections else self.get_sections(course))
docs: Internal use. Creates all variables in the problem instance for the given
          courses. If given a dict of {course: sections}, will use the provided sections.