code: def generate_sub_codons_left(codons_dict):
      
      sub_codons_left = {}
      for aa in codons_dict.keys():
          sub_codons_left[aa] = list(set([x[0] for x in codons_dict[aa]] + [x[:2] for x in codons_dict[aa]]))
          
      return sub_codons_left
docs: Generate the sub_codons_left dictionary of codon prefixes.
  
      Parameters
      ----------
      codons_dict : dict
          Dictionary, keyed by the allowed 'amino acid' symbols with the values 
          being lists of codons corresponding to the symbol.
  
      Returns
      -------
      sub_codons_left : dict
          Dictionary of the 1 and 2 nucleotide prefixes (read from 5') for 
          each codon in an 'amino acid' grouping