code: def get_default_class1_models_dir(test_exists=True):
      
      if _MHCFLURRY_DEFAULT_CLASS1_MODELS_DIR:
          result = join(get_downloads_dir(), _MHCFLURRY_DEFAULT_CLASS1_MODELS_DIR)
          if test_exists and not exists(result):
              raise IOError("No such directory: %s" % result)
          return result
      else:
          return get_path("models_class1", "models", test_exists=test_exists)
docs: Return the absolute path to the default class1 models dir.
  
      If environment variable MHCFLURRY_DEFAULT_CLASS1_MODELS is set to an
      absolute path, return that path. If it's set to a relative path (i.e. does
      not start with /) then return that path taken to be relative to the mhcflurry
      downloads dir.
  
      If environment variable MHCFLURRY_DEFAULT_CLASS1_MODELS is NOT set,
      then return the path to downloaded models in the "models_class1" download.
  
      Parameters
      ----------
  
      test_exists : boolean, optional
          Whether to raise an exception of the path does not exist
  
      Returns
      -------
      string : absolute path