code: def transform(self, raw_X, y=None):
          
          return [self._extract_features(sequence1, sequence2) for sequence1, sequence2 in raw_X]
docs: Transform sequence pairs to feature arrays that can be used as input to `Hacrf` models.
  
          Parameters
          ----------
          raw_X : List of (sequence1_n, sequence2_n) pairs, one for each training example n.
          y : (ignored)
  
          Returns
          -------
           X : List of numpy ndarrays, each with shape = (I_n, J_n, K), where I_n is the length of sequence1_n, J_n is the
              length of sequence2_n, and K is the number of features.
              Feature matrix list, for use with estimators or further transformers.