code: def _update_with_merge_lists(self, other, key, val=None, **options):
      
      _update_with_merge(self, other, key, val=val, merge_lists=True, **options)
docs: Similar to _update_with_merge but merge lists always.
  
      :param self: mapping object to update with 'other'
      :param other: mapping object to update 'self'
      :param key: key of mapping object to update
      :param val: value to update self alternatively
  
      :return: None but 'self' will be updated