def back_transcribe(rna):
 if isinstance(rna, Seq):
  return rna.back_transcribe()
 elif isinstance(rna, MutableSeq):
  return rna.toseq().back_transcribe()
 else:
  return rna.replace('U', 'T').replace('u', 't')

def back_transcribe ( rna ) : if isinstance ( rna , Seq ) : return rna . back_transcribe ( ) elif isinstance ( rna , MutableSeq ) : return rna . toseq ( ) . back_transcribe ( ) else : return rna . replace ( 'U' , 'T' ) . replace ( 'u' , 't' )
back-transcribes an rna sequence into dna .