'Makes a UploadWorkItem containing the given rows, with the given keys.
Args:
key_start: The start key for the UploadWorkItem.
key_end: The end key for the UploadWorkItem.
rows: A list of the rows for the UploadWorkItem.
progress_key: The progress key for the UploadWorkItem
Returns:
An UploadWorkItem instance for the given batch.'

def _MakeItem(self, key_start, key_end, rows, progress_key=None):

    assert rows
    item = UploadWorkItem(self.request_manager, self.progress_queue, rows, key_start, key_end, progress_key=progress_key)
    return item
