code: def insert_after(sequence, offset, new_residues):
      
      assert 0 <= offset < len(sequence), \
          "Invalid position %d for sequence of length %d" % (
              offset, len(sequence))
      prefix = sequence[:offset + 1]
      suffix = sequence[offset + 1:]
      return prefix + new_residues + suffix
docs: Mutate the given sequence by inserting the string `new_residues` after
      `offset`.
  
      Parameters
      ----------
      sequence : sequence
          String of amino acids or DNA bases
  
      offset : int
          Base 0 offset from start of sequence, after which we should insert
          `new_residues`.
  
      new_residues : sequence