code: def validate_subset(df, subset):
      if subset is None:
          return subset
      if not is_list_like(subset):
          subset = [subset]
      else:
          subset = list(subset)
  
      for s in subset:
          if s not in df.dtypes:
              raise KeyError(pd.Index([s]))
  
      return subset
  
imports: import inspect
  import numpy
  import pandas
  from pandas.api.types import is_list_like
  from ...config import options
  from ...core import OutputType, recursive_tile
  from ...core.operand import OperandStage, MapReduceOperand
  from ...serialization.serializables import AnyField, Int32Field, StringField, KeyField
  from ...utils import ceildiv, has_unknown_shape, lazy_import
  from ..initializer import DataFrame
  from ..operands import DataFrameOperandMixin, DataFrameShuffleProxy
label_desc: Use image node_id 1 for calling a global function with example usage: validate_subset(df, subset) and returns: subset, subset