def preproc_seq(IDs,CDS):
    """
    Transforms CDS to space-delimited string of codons
    Input:
        list of sequences
    Outputs:
        list of sequences as space-delimited codons"""
    codons = []
    final_ids=[]
    for i in range(len(CDS)):
            seq = CDS[i]
            ID= IDs[i]
            if len(seq)%3 !=0:  ## only CDS that are exact multiple of 3
                print(f'{IDs[i]} CDS is not multiple of 3....Skipping Sequence')
                continue
            cod_list = []
            for j in range(0, len(seq),3):
                codon = seq[j:j+3]
                cod_list.append(codon)
              
            cods = " ".join(cod_list)
            final_ids.append(ID)
            codons.append(cods)
    return (codons,final_ids)