code: def from_json(json):
          
          segments = [Segment.from_json(s) for s in json['segments']]
          return Track(json['name'], segments).compute_metrics()
docs: Creates a Track from a JSON file.
  
          No preprocessing is done.
  
          Arguments:
              json: map with the keys: name (optional) and segments.
          Return:
              A track instance