kaldi command pipeline expression in python

kaldi_io_mechanisms.py

delta_command = "compute-mfcc-feats --config=conf/mfcc.conf scp,p:wav_test.scp ark:- | add-deltas ark:- ark:- |"
delta_feats_rspecifier = (
     f'ark:{delta_command}'
  )

mfcc_command = "compute-mfcc-feats --config=conf/mfcc.conf scp,p:wav_test.scp ark:- |"
mfcc_feats_rspecifier = (
     f'ark:{mfcc_command}'
  )

mfcc_pitch_command = "compute-kaldi-pitch-feats --config=conf/pitch.conf scp,p:wav_test.scp ark:- | process-kaldi-pitch-feats ark:- ark:- |"
mfcc_pitch_feats_rspecifier = (
  "ark,s,cs:"+mfcc_pitch_command
  )

paste_command = f"paste-feats --length-tolerance=2 '{mfcc_feats_rspecifier}' '{mfcc_pitch_feats_rspecifier}' ark:- |"
paste_feats_rspecifier = (
     "ark:"+paste_command
     )

copy_command = f"copy-feats --compress=true \"{paste_feats_rspecifier}\" ark,scp:raw_mfcc_pitch.ark,raw_mfcc_pitch.scp"
copy_feats_rspecifier = (
     copy_command
     )

splice_command = f"splice-feats \"{paste_feats_rspecifier}\" ark:- |"
splice_feats_rspecifier = (
     "ark:"+splice_command
     )

trans_command = f"{splice_command} transform-feats model/final.mat ark:- ark:- |"
trans_feats_rspecifier = (
     "ark,s,cs:"+trans_command
     )