docs: def findCodons(seq, codons):
      """
      Find all instances of the codons in 'codons' in the given sequence.
  
      seq: A Bio.Seq.Seq instance.
      codons: A set of codon strings.
  
      Return: a generator yielding matching codon offsets.
      """
      seqLen = len(seq)
      start = 0
      while start < seqLen:
          triplet = str(seq[start:start + 3])
          if triplet in codons:
              yield start
          start = start + 3