code: def open_writer(self, reopen=False, endpoint=None, **kwargs):
          
          tunnel = self._create_volume_tunnel(endpoint=endpoint)
          upload_id = self._upload_id if not reopen else None
          upload_session = tunnel.create_upload_session(volume=self.volume.name, partition_spec=self.name,
                                                        upload_id=upload_id, **kwargs)
          file_dict = dict()
  
          class FilesWriter(object):
              @property
              def status(self):
                  return upload_session.status
  
              @staticmethod
              def open(file_name, **kwargs):
                  if file_name in file_dict:
                      return file_dict[file_name]
                  writer = upload_session.open(file_name, **kwargs)
                  file_dict[file_name] = writer
                  return writer
  
              @staticmethod
              def write(file_name, buf, **kwargs):
                  writer = FilesWriter.open(file_name, **kwargs)
                  writer.write(buf)
  
              @staticmethod
              def close():
                  for w in six.itervalues(file_dict):
                      w.close()
  
                  upload_session.commit(list(six.iterkeys(file_dict)))
  
              def __enter__(self):
                  return self
  
              def __exit__(self, exc_type, exc_val, exc_tb):
                  self.close()
  
          return FilesWriter()
docs: Open a volume partition to write to. You can use `open` method to open a file inside the volume and write to it,
          or use `write` method to write to specific files.
  
          :param bool reopen: whether we need to open an existing write session
          :param str endpoint: tunnel service URL
          :param compress_option: the compression algorithm, level and strategy
          :type compress_option: :class:`odps.tunnel.CompressOption`
          :Example:
          >>> with partition.open_writer() as writer:
          >>>     writer.open('file1').write('some content')
          >>>     writer.write('file2', 'some content')