code: def _raise_on_mode(self, mode):
          
          valid_modes = [
              'random_sample',
              'random_sample_per_pix',
              'samples',
              'median',
              'mean',
              'best',
              'percentile']
  
          if mode not in valid_modes:
              raise ValueError(
                  '"{}" is not a valid `mode`. Valid modes are:\n'
                  '  {}'.format(mode, valid_modes)
              )
docs: Checks that the provided query mode is one of the accepted values. If
          not, raises a :obj:`ValueError`.