class_docstr: SortKey class to convert between different sort args formats.
class_docstr_tok: ["SortKey","class","to","convert","between","different","sort","args","formats","."]
code: def get_columns(self) -> List[str]:
      return self._columns
  
imports: from typing import TYPE_CHECKING, List, Optional, Tuple, TypeVar, Union
  import numpy
  from ray.data._internal.block_list import BlockList
  from ray.data._internal.delegating_block_builder import DelegatingBlockBuilder
  from ray.data._internal.execution.interfaces import TaskContext
  from ray.data._internal.progress_bar import ProgressBar
  from ray.data._internal.push_based_shuffle import PushBasedShufflePlan
  from ray.data._internal.remote_fn import cached_remote_fn
  from ray.data._internal.shuffle import ShuffleOp, SimpleShufflePlan
  from ray.data.block import Block, BlockAccessor, BlockExecStats, BlockMetadata
  from ray.data.context import DataContext
  from ray.types import ObjectRef
label_desc: Use image node_id 2 for calling the SortKey obj's underlying member method code with example usage: obj.get_columns() and returns: self