code: def _spill(self):
          
          global MemoryBytesSpilled, DiskBytesSpilled
          if self._file is None:
              self._open_file()
  
          used_memory = get_used_memory()
          pos = self._file.tell()
          self._ser.dump_stream(self.values, self._file)
          self.values = []
          gc.collect()
          DiskBytesSpilled += self._file.tell() - pos
          MemoryBytesSpilled += max(used_memory - get_used_memory(), 0) << 20
docs: dump the values into disk