code: def _get_first_slice(op, df, end):
      if op.method == "bfill":
          if op.output_types[0] == OutputType.series:
              return df.iloc[:end]
          else:
              if op.axis == 1:
                  return df.iloc[:, :end]
              else:
                  return df.iloc[:end, :]
      else:
          if op.output_types[0] == OutputType.series:
              return df.iloc[-end:]
          else:
              if op.axis == 1:
                  return df.iloc[:, -end:]
              else:
                  return df.iloc[-end:, :]
  
imports: import itertools
  import numpy
  import pandas
  from ...None import opcodes
  from ...config import options
  from ...core import ENTITY_TYPE, Entity, OutputType, get_output_types
  from ...core.operand import OperandStage
  from ...serialization.serializables import StringField, AnyField, BoolField, Int64Field
  from ..align import align_dataframe_dataframe, align_dataframe_series, align_series_series
  from ..core import DATAFRAME_TYPE, SERIES_TYPE
  from ..operands import DataFrameOperandMixin, DataFrameOperand
  from ..utils import validate_axis
label_desc: Use image node_id 10 for calling the FillNA obj's underlying member method code with example usage: obj._get_first_slice(op, df, end) and returns: df, df, df, df, df, df