code: def __call__(self, input_df):
      test_df = build_df(input_df)
      test_df = test_df.stack(level=self._level, dropna=self._dropna)
      if self._dropna:
          size = np.nan
      else:
          size = self._calc_size(
              input_df.shape[0], self._level, input_df.dtypes
          )
      if test_df.ndim == 1:
          shape = (size,)
          return self.new_series(
              [input_df],
              shape=shape,
              dtype=test_df.dtype,
              index_value=parse_index(test_df.index, input_df),
              name=test_df.name,
          )
      else:
          shape = (size, test_df.shape[1])
          return self.new_dataframe(
              [input_df],
              shape=shape,
              dtypes=test_df.dtypes,
              index_value=parse_index(test_df.index, input_df),
              columns_value=parse_index(
                  test_df.columns, store_data=True
              ),
          )
  
imports: from typing import Union, List
  import numpy
  import pandas
  from ...None import opcodes
  from ...core import recursive_tile
  from ...serialization.serializables import KeyField, AnyField, BoolField
  from ...utils import has_unknown_shape
  from ..operands import DataFrameOperand, DataFrameOperandMixin
  from ..utils import build_df, parse_index
label_desc: Use image node_id 7 for calling the DataFrameStack obj's underlying member method code with example usage: obj.__call__(input_df) and returns: self, self