code: def get_codon(seq, codon_no, start_offset):
      
      seq = seq.replace("-","")
      codon_start_pos = int(codon_no - 1)*3 - start_offset
      codon = seq[codon_start_pos:codon_start_pos + 3]
      return codon
docs: This function takes a sequece and a codon number and returns the codon
      found in the sequence at that position