code: def get_from_metadata_file(cls, dirpath, key):
          
          fullpath = os.path.join(dirpath, cls.metadata_filename)
          if os.path.exists(fullpath):
              d = pickle.load(open(fullpath, 'rb'))
              return d[key]
          else:
              raise FileNotFoundError(
                  "No such file: {0}".format(fullpath))
docs: Get value of key in metadata file dict.