code: def update(self, key_vals=None, overwrite=True):
          
          if not key_vals:
              return
          write_items = self._update(key_vals, overwrite)
          self._root._root_set(self._path, write_items)
          self._root._write(commit=True)
docs: Locked keys will be overwritten unless overwrite=False.
  
          Otherwise, written keys will be added to the "locked" list.