class_docstr: Indexer mixin
  
  Mixin for handling indexers.
  
  .. note::
     To use this mixin the instance inheriting it must set the
      ``indexer`` or ``indexers`` attribute in ``__init__`` (not both).
docstr: Return list of indexers
docstr_tok: ["Return","list","of","indexers"]
code: def _get_indexers(self):
      """Return list of indexers"""
      if not self.__indexer__:
          raise AttributeError(
              "No indexer or indexers attribute available"
          )
      indexers = [getattr(self, "indexer", None)]
      if None in indexers:
          indexers = getattr(self, "indexers", [None])
      return indexers
  
imports: import warnings
  from abc import abstractmethod
  import numpy
  from ._base_functions import check_stack, check_params
  from ..None import config
  from ..utils.exceptions import ParallelProcessingError
  from ..externals.sklearn.base import clone, BaseEstimator
label_desc: Use image node_id 3 for calling the IndexMixin obj's underlying member method code with example usage: obj._get_indexers() and returns: indexers