code: def add_molfile(self, molfile, data):
          
          if not isinstance(molfile, Molfile):
              raise ValueError('Not a Molfile type: "{}"'.format(type(molfile)))
  
          if not isinstance(data, dict):
              raise ValueError('Not a dict type: "{}"'.format(type(data)))
  
          entry_ids = sorted(self.keys(), key=lambda x: int(x))
          if entry_ids:
              last_entry_id = str(entry_ids[-1])
          else:
              last_entry_id = '0'
  
          new_entry_id = str(int(last_entry_id) + 1)
          self[new_entry_id] = OrderedDict()
          self[new_entry_id]['molfile'] = molfile
          self[new_entry_id]['data'] = data
docs: Add ``Molfile`` and data to ``SDfile`` object.
  
          :param molfile: ``Molfile`` instance.
          :type molfile: :class:`~ctfile.ctfile.Molfile`.
          :param dict data: Data associated with ``Molfile`` instance. 
          :return: None.
          :rtype: :py:obj:`None`.